Android中的拖拽及嵌套滑动

15_Android中的拖拽及嵌套滑动

• 拖拽和嵌套滑动
• • 拖拽
  • 为什么要这两个东西，而不是一个？
  • 嵌套滑动

拖拽和嵌套滑动

拖拽

OnDragListener

• 通过startDrag()来启动拖拽
• 用 setOnDragListener()来监听
  • OnDragListener 内部只有一个方法：onDrag()
  • onDragEvent()方法也会收到拖拽回调(界面中的每个View都会收到)

ViewDragHelper

• 需要创建一个 ViewDragHelper 和 Callback()
• 需要写在 ViewGroup 里面，重写 onInterceptTouchEvent()和 onTouchevent()

为什么要这两个东西，而不是一个？

• OnDragListener

  • API 11加入的工具类，用于拖拽操作。
  • 使用场景：用户的「拖起-> 放下」操作，重在内容的移动。可以附加拖拽数据
  • 不需要写自定义View，使用startDrag() / startDragAndDrop()手动开启拖拽
  • 拖拽的原理是创造出一个图像在屏幕的最上层，用户的手指拖着图像移动

• ViewDragHelper

  • 2015年的support v4包中新增的工具类，用于拖拽操作。
  • 使用场景：用户拖动ViewGroup中的某个子View
  • 需要应用在自定义 ViewGroup 中调用 ViewDragHelper.shouldInterceptTouchEvent()和 processTouchEvent()，程序会自动开启拖拽
  • 拖拽的原理是实时修改被拖拽的子View的mLeft, mTop, mRight, mBottom值

嵌套滑动

嵌套滑动的场景

• 不同向嵌套

  • onInterceptTouchEvent 父 View 拦截
  • requestDisallowInterceptTouchEvent()子 View 阻止父 View 拦截

• 同向嵌套

  • 父View会彻底卡住子View

    • 原因：抢夺条件一致，但父View的onInterceptTouchEvent（）早于子View的 dispatchTouchEvent（）

  • 本质上是策略问题：嵌套状态下用户手指滑动，他是想滑谁？

    • 场景一：NestedScrollView
      • 子View能滑动的时候，滑子View；滑不动的时候，滑父View
    • 场景二：Google的样例
      • 父View展开的时候：
        • 上滑：优先滑父View
        • 下滑：滑不动（所以可以说还是优先滑父View）
      • 父View半展开的时候：
        • 向上：优先滑父View，滑到父View完全收齐之后开始滑子View
        • 向下：滑父View，滑到父View完全展开之后开始滑子View
      • 父View收起的时候：
        • 上滑：滑子View （所以可以说是优先滑子View）
        • 下滑：优先滑子View，滑到子View顶部的时候开始滑父View

  • 解决方案：实现策略一一父View、子View谁来消费事件可以实时协商

  • 实现？

    • 其实大多数场景，SDK就解决了
      • 案例1：ScrollView嵌套：没法滑动
      • 案例2：换成NestedScrollView :可以滑动
    • 自己实现？
      • 案例3：按照课上代码，实现NestedScrollingChild2接口来实现自定义的嵌套滑动逻辑

OnDragListener范例1

public class DragListenerGridView extends ViewGroup {
    private static final int COLUMNS = 2;
    private static final int ROWS = 3;

    ViewConfiguration viewConfiguration;
    OnDragListener dragListener = new HenDragListener();
    View draggedView;
    List<View> orderedChildren = new ArrayList<>();

    public DragListenerGridView(Context context, AttributeSet attrs) {
        super(context, attrs);
        viewConfiguration = ViewConfiguration.get(context);
        setChildrenDrawingOrderEnabled(true);
    }

    @Override
    protected void onFinishInflate() {
        super.onFinishInflate();
        for (int i = 0; i < getChildCount(); i++) {
            View child = getChildAt(i);
            orderedChildren.add(child); // 初始化位置
            child.setOnLongClickListener(new OnLongClickListener() {
                @Override
                public boolean onLongClick(View v) {
                    draggedView = v;
                    v.startDrag(null, new DragShadowBuilder(v), v, 0);
                    return false;
                }
            });
            child.setOnDragListener(dragListener);
        }
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        int specWidth = MeasureSpec.getSize(widthMeasureSpec);
        int specHeight = MeasureSpec.getSize(heightMeasureSpec);
        int childWidth = specWidth / COLUMNS;
        int childHeight = specHeight / ROWS;

        measureChildren(MeasureSpec.makeMeasureSpec(childWidth, MeasureSpec.EXACTLY),
                MeasureSpec.makeMeasureSpec(childHeight, MeasureSpec.EXACTLY));

        setMeasuredDimension(specWidth, specHeight);
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        int count = getChildCount();
        int childLeft;
        int childTop;
        int childWidth = getWidth() / COLUMNS;
        int childHeight = getHeight() / ROWS;
        for (int index = 0; index < count; index++) {
            View child = getChildAt(index);
            childLeft = index % 2 * childWidth;
            childTop = index / 2 * childHeight;
            child.layout(0, 0, childWidth, childHeight);
//            child.layout(childLeft, childTop, childWidth, childHeight);
            child.setTranslationX(childLeft);
            child.setTranslationY(childTop);
        }
    }

    private class HenDragListener implements OnDragListener {
        @Override
        public boolean onDrag(View v, DragEvent event) {
            switch (event.getAction()) {
                case DragEvent.ACTION_DRAG_STARTED:
                    if (event.getLocalState() == v) {
                        v.setVisibility(INVISIBLE);
                    }
                    break;
                case DragEvent.ACTION_DRAG_ENTERED:
                    if (event.getLocalState() != v) {
                        sort(v);
                    }
                    break;
                case DragEvent.ACTION_DRAG_EXITED:
                    break;
                case DragEvent.ACTION_DRAG_ENDED:
                    v.setVisibility(VISIBLE);
                    break;
            }
            return true;
        }
    }

    private void sort(View targetView) {
        int draggedIndex = -1;
        int targetIndex = -1;
        for (int i = 0; i < getChildCount(); i++) {
            View child = orderedChildren.get(i);
            if (targetView == child) {
                targetIndex = i;
            } else if (draggedView == child) {
                draggedIndex = i;
            }
        }
        if (targetIndex < draggedIndex) {
            orderedChildren.remove(draggedIndex);
            orderedChildren.add(targetIndex, draggedView);
        } else if (targetIndex > draggedIndex) {
            orderedChildren.remove(draggedIndex);
            orderedChildren.add(targetIndex, draggedView);
        }
        int childLeft;
        int childTop;
        int childWidth = getWidth() / COLUMNS;
        int childHeight = getHeight() / ROWS;
        for (int index = 0; index < getChildCount(); index++) {
            View child = orderedChildren.get(index);
            childLeft = index % 2 * childWidth;
            childTop = index / 2 * childHeight;
            child.animate()
                    .translationX(childLeft)
                    .translationY(childTop)
                    .setDuration(150);
        }
    }
}

drag_listener_grid_view.xml

<?xml version="1.0" encoding="utf-8"?>
<com.hencoder.a15_drag_nestedscroll.view.drag.DragListenerGridView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <View
        android:id="@+id/view"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#EF5350" />

    <View
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#9C27B0" />

    <View
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#1E88E5" />

    <View
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#00695C" />

    <View
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#FDD835" />

    <View
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#546E7A" />

</com.hencoder.a15_drag_nestedscroll.view.drag.DragListenerGridView>

OnDragListener范例2

public class DragToCollectLayout extends RelativeLayout {
    ImageView avatarView;
    ImageView logoView;
    LinearLayout collectorLayout;

    OnLongClickListener dragStarter = new OnLongClickListener() {
        @SuppressLint("Range")
        @Override
        public boolean onLongClick(View v) {
            ClipData imageData = ClipData.newPlainText("name", v.getContentDescription());
            v.setAlpha((float) 0.5);
            return ViewCompat.startDragAndDrop(v, imageData, new DragShadowBuilder(v), null, 0);
        }
    };
    OnDragListener dragListener = new CollectListener();

    public DragToCollectLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    protected void onFinishInflate() {
        super.onFinishInflate();

        avatarView = findViewById(R.id.avatarView);
        logoView = findViewById(R.id.logoView);
        collectorLayout = findViewById(R.id.collectorLayout);

        avatarView.setOnLongClickListener(dragStarter);
        logoView.setOnLongClickListener(dragStarter);
        collectorLayout.setOnDragListener(dragListener);
    }

    class CollectListener implements OnDragListener {
        @Override
        public boolean onDrag(View v, DragEvent event) {
            switch (event.getAction()) {
                case DragEvent.ACTION_DROP:
                    if (v instanceof LinearLayout) {
                        LinearLayout layout = (LinearLayout) v;
                        TextView textView = new TextView(getContext());
                        textView.setTextSize(16);
                        textView.setText(event.getClipData().getItemAt(0).getText());
                        layout.addView(textView);
                    }
                    break;
            }
            return true;
        }
    }

}

drag_to_collect.xml

<?xml version="1.0" encoding="utf-8"?>
<com.hencoder.a15_drag_nestedscroll.view.drag.DragToCollectLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <ImageView
            android:id="@+id/avatarView"
            android:layout_width="0dp"
            android:layout_height="120dp"
            android:layout_weight="1"
            android:src="@drawable/avatar_rengwuxian"
            android:contentDescription="Avatar" />

        <ImageView
            android:id="@+id/logoView"
            android:layout_width="0dp"
            android:layout_height="120dp"
            android:layout_weight="1"
            android:src="@drawable/google_logo"
            android:contentDescription="Logo" />
    </LinearLayout>

    <LinearLayout
        android:id="@+id/collectorLayout"
        android:layout_width="match_parent"
        android:layout_height="80dp"
        android:layout_alignParentBottom="true"
        android:background="#78909C"
        android:orientation="horizontal" />

</com.hencoder.a15_drag_nestedscroll.view.drag.DragToCollectLayout>

ViewDragHelper范例1

public class DragHelperGridView extends ViewGroup {
    private static final int COLUMNS = 2;
    private static final int ROWS = 3;

    ViewDragHelper dragHelper;

    public DragHelperGridView(Context context, AttributeSet attrs) {
        super(context, attrs);
        dragHelper = ViewDragHelper.create(this, new DragCallback());
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        int specWidth = MeasureSpec.getSize(widthMeasureSpec);
        int specHeight = MeasureSpec.getSize(heightMeasureSpec);
        int childWidth = specWidth / COLUMNS;
        int childHeight = specHeight / ROWS;

        measureChildren(MeasureSpec.makeMeasureSpec(childWidth, MeasureSpec.EXACTLY),
                MeasureSpec.makeMeasureSpec(childHeight, MeasureSpec.EXACTLY));

        setMeasuredDimension(specWidth, specHeight);
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        int count = getChildCount();
        int childLeft;
        int childTop;
        int childWidth = getWidth() / COLUMNS;
        int childHeight = getHeight() / ROWS;
        for (int index = 0; index < count; index++) {
            View child = getChildAt(index);
            childLeft = index % 2 * childWidth;
            childTop = index / 2 * childHeight;
            child.layout(childLeft, childTop, childLeft + childWidth, childTop + childHeight);
        }
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        return dragHelper.shouldInterceptTouchEvent(ev);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        dragHelper.processTouchEvent(event);
        return true;
    }

    @Override
    public void computeScroll() {
        if (dragHelper.continueSettling(true)) {
            ViewCompat.postInvalidateOnAnimation(this);
        }
    }

    private class DragCallback extends ViewDragHelper.Callback {
        float capturedLeft;
        float capturedTop;

        @Override
        public boolean tryCaptureView(@NonNull View child, int pointerId) {
            return true;
        }

        @Override
        public void onViewDragStateChanged(int state) {
            if (state == ViewDragHelper.STATE_IDLE) {
                View capturedView = dragHelper.getCapturedView();
                if (capturedView != null) {
                    capturedView.setElevation(capturedView.getElevation() - 1);
                }
            }
        }

        @Override
        public int clampViewPositionHorizontal(@NonNull View child, int left, int dx) {
            return left;
        }

        @Override
        public int clampViewPositionVertical(@NonNull View child, int top, int dy) {
            return top;
        }

        @Override
        public void onViewCaptured(@NonNull View capturedChild, int activePointerId) {
            capturedChild.setElevation(getElevation() + 1);
            capturedLeft = capturedChild.getLeft();
            capturedTop = capturedChild.getTop();
        }

        @Override
        public void onViewPositionChanged(@NonNull View changedView, int left, int top, int dx, int dy) {
        }

        @Override
        public void onViewReleased(@NonNull View releasedChild, float xvel, float yvel) {
            dragHelper.settleCapturedViewAt((int) capturedLeft, (int) capturedTop);
            postInvalidateOnAnimation();
        }
    }
}

drag_helper_grid_view.xml

<?xml version="1.0" encoding="utf-8"?>
<com.hencoder.a15_drag_nestedscroll.view.drag.DragHelperGridView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <View
        android:id="@+id/view"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#EF5350" />

    <View
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#9C27B0" />

    <View
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#1E88E5" />

    <View
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#00695C" />

    <View
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#FDD835" />

    <View
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#546E7A" />

</com.hencoder.a15_drag_nestedscroll.view.drag.DragHelperGridView>

ViewDragHelper范例2

public class DragUpDownLayout extends FrameLayout {
    View view;
    ViewDragHelper dragHelper;
    ViewDragHelper.Callback dragListener = new DragListener();
    ViewConfiguration viewConfiguration;

    public DragUpDownLayout(@NonNull Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);

        dragHelper = ViewDragHelper.create(this, dragListener);
        viewConfiguration = ViewConfiguration.get(context);
    }

    @Override
    protected void onFinishInflate() {
        super.onFinishInflate();
        view = findViewById(R.id.view);
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        return dragHelper.shouldInterceptTouchEvent(ev);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        dragHelper.processTouchEvent(event);
        return true;
    }

    @Override
    public void computeScroll() {
        if (dragHelper.continueSettling(true)) {
            ViewCompat.postInvalidateOnAnimation(this);
        }
    }

    class DragListener extends ViewDragHelper.Callback {
        @Override
        public boolean tryCaptureView(@NonNull View child, int pointerId) {
            return child == view;
        }

        @Override
        public int clampViewPositionVertical(@NonNull View child, int top, int dy) {
            return top;
        }

        @Override
        public void onViewReleased(@NonNull View releasedChild, float xvel, float yvel) {
            if (Math.abs(yvel) > viewConfiguration.getScaledMinimumFlingVelocity()) {
                if (yvel > 0) {
                    dragHelper.settleCapturedViewAt(0, getHeight() - releasedChild.getHeight());
                } else {
                    dragHelper.settleCapturedViewAt(0, 0);
                }
            } else {
                if (releasedChild.getTop() < getHeight() - releasedChild.getBottom()) {
                    dragHelper.settleCapturedViewAt(0, 0);
                } else {
                    dragHelper.settleCapturedViewAt(0, getHeight() - releasedChild.getHeight());
                }
            }
            postInvalidateOnAnimation();
        }
    }

}

drag_up_down.xml

<?xml version="1.0" encoding="utf-8"?>
<com.hencoder.a15_drag_nestedscroll.view.drag.DragUpDownLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <View
        android:id="@+id/view"
        android:layout_width="match_parent"
        android:layout_height="200dp"
        android:background="#388E3C"/>

</com.hencoder.a15_drag_nestedscroll.view.drag.DragUpDownLayout>

案例1
scroll_view.xml

<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">

        <View
            android:layout_width="match_parent"
            android:layout_height="400dp"
            android:background="@color/colorAccent" />

        <ScrollView
            android:layout_width="match_parent"
            android:layout_height="400dp">

            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:orientation="vertical">

                <View
                    android:layout_width="match_parent"
                    android:layout_height="100dp"
                    android:background="#22000000"/>

                <View
                    android:layout_width="match_parent"
                    android:layout_height="100dp"
                    android:background="#44000000"/>

                <View
                    android:layout_width="match_parent"
                    android:layout_height="100dp"
                    android:background="#66000000"/>

                <View
                    android:layout_width="match_parent"
                    android:layout_height="100dp"
                    android:background="#88000000"/>

                <View
                    android:layout_width="match_parent"
                    android:layout_height="100dp"
                    android:background="#aa000000"/>

                <View
                    android:layout_width="match_parent"
                    android:layout_height="100dp"
                    android:background="#22ff0000"/>

                <View
                    android:layout_width="match_parent"
                    android:layout_height="100dp"
                    android:background="#44ff0000"/>

            </LinearLayout>

        </ScrollView>

    </LinearLayout>

</ScrollView>

案例2
nested_scroll_view.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.core.widget.NestedScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">

        <View
            android:layout_width="match_parent"
            android:layout_height="400dp"
            android:background="@color/colorAccent" />

        <androidx.core.widget.NestedScrollView
            android:layout_width="match_parent"
            android:layout_height="400dp">

            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:orientation="vertical">

                <View
                    android:layout_width="match_parent"
                    android:layout_height="100dp"
                    android:background="#22000000"/>

                <View
                    android:layout_width="match_parent"
                    android:layout_height="100dp"
                    android:background="#44000000"/>

                <View
                    android:layout_width="match_parent"
                    android:layout_height="100dp"
                    android:background="#66000000"/>

                <View
                    android:layout_width="match_parent"
                    android:layout_height="100dp"
                    android:background="#88000000"/>

                <View
                    android:layout_width="match_parent"
                    android:layout_height="100dp"
                    android:background="#aa000000"/>

                <View
                    android:layout_width="match_parent"
                    android:layout_height="100dp"
                    android:background="#22ff0000"/>

                <View
                    android:layout_width="match_parent"
                    android:layout_height="100dp"
                    android:background="#44ff0000"/>

            </LinearLayout>

        </androidx.core.widget.NestedScrollView>

    </LinearLayout>

</androidx.core.widget.NestedScrollView>

案例3
nested_scalable_image_view.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.core.widget.NestedScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">

        <View
            android:layout_width="match_parent"
            android:layout_height="400dp"
            android:background="@color/colorAccent" />

        <com.hencoder.a15_drag_nestedscroll.view.nested_scroll.ScalableImageView
            android:layout_width="match_parent"
            android:layout_height="800dp" />

    </LinearLayout>

</androidx.core.widget.NestedScrollView>

public class ScalableImageView extends View implements NestedScrollingChild2 {
    private static final float IMAGE_WIDTH = Utils.dpToPixel(300);
    private static final float OVER_SCALE_FACTOR = 1.5f;

    Bitmap bitmap;
    Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);

    float offsetX;
    float offsetY;
    float originalOffsetX;
    float originalOffsetY;
    float smallScale;
    float bigScale;
    boolean big;
    float currentScale;
    ObjectAnimator scaleAnimator;
    GestureDetectorCompat detector;
    HenGestureListener gestureListener = new HenGestureListener();
    HenFlingRunner henFlingRunner = new HenFlingRunner();
    ScaleGestureDetector scaleDetector;
    HenScaleListener henScaleListener = new HenScaleListener();
    OverScroller scroller;
    NestedScrollingChildHelper childHelper;

    public ScalableImageView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);

        bitmap = Utils.getAvatar(getResources(), (int) IMAGE_WIDTH);
        detector = new GestureDetectorCompat(context, gestureListener);
        scroller = new OverScroller(context);
        scaleDetector = new ScaleGestureDetector(context, henScaleListener);
        childHelper = new NestedScrollingChildHelper(this);
        childHelper.setNestedScrollingEnabled(true);
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);

        originalOffsetX = ((float) getWidth() - bitmap.getWidth()) / 2;
        originalOffsetY = ((float) getHeight() - bitmap.getHeight()) / 2;

        if ((float) bitmap.getWidth() / bitmap.getHeight() > (float) getWidth() / getHeight()) {
            smallScale = (float) getWidth() / bitmap.getWidth();
            bigScale = (float) getHeight() / bitmap.getHeight() * OVER_SCALE_FACTOR;
        } else {
            smallScale = (float) getHeight() / bitmap.getHeight();
            bigScale = (float) getWidth() / bitmap.getWidth() * OVER_SCALE_FACTOR;
        }
        currentScale = smallScale;
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        boolean result = scaleDetector.onTouchEvent(event);
        if (!scaleDetector.isInProgress()) {
            result = detector.onTouchEvent(event);
            childHelper.startNestedScroll(ViewCompat.SCROLL_AXIS_VERTICAL);
        }

        return result;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        float scaleFraction = (currentScale - smallScale) / (bigScale - smallScale);
        canvas.translate(offsetX * scaleFraction, offsetY * scaleFraction);
        canvas.scale(currentScale, currentScale, getWidth() / 2f, getHeight() / 2f);
        canvas.drawBitmap(bitmap, originalOffsetX, originalOffsetY, paint);
    }

    private float getCurrentScale() {
        return currentScale;
    }

    private void setCurrentScale(float currentScale) {
        this.currentScale = currentScale;
        invalidate();
    }

    private ObjectAnimator getScaleAnimator() {
        if (scaleAnimator == null) {
            scaleAnimator = ObjectAnimator.ofFloat(this, "currentScale", 0);
        }
        scaleAnimator.setFloatValues(smallScale, bigScale);
        return scaleAnimator;
    }

    @Override
    public boolean startNestedScroll(int axes, int type) {
        return childHelper.startNestedScroll(axes, type);
    }

    @Override
    public void stopNestedScroll(int type) {
        childHelper.stopNestedScroll(type);
    }

    @Override
    public boolean hasNestedScrollingParent(int type) {
        return childHelper.hasNestedScrollingParent(type);
    }

    @Override
    public boolean dispatchNestedScroll(int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed, @Nullable int[] offsetInWindow, int type) {
        return childHelper.dispatchNestedScroll(dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed, offsetInWindow, type);
    }

    @Override
    public boolean dispatchNestedPreScroll(int dx, int dy, @Nullable int[] consumed, @Nullable int[] offsetInWindow, int type) {
        return childHelper.dispatchNestedPreScroll(dx, dy, consumed, offsetInWindow, type);
    }

    class HenGestureListener extends GestureDetector.SimpleOnGestureListener {

        @Override
        public boolean onDown(MotionEvent e) {
            return true;
        }

        @Override
        public void onShowPress(MotionEvent e) {

        }

        @Override
        public boolean onSingleTapUp(MotionEvent e) {
            return false;
        }

        @Override
        public boolean onScroll(MotionEvent down, MotionEvent event, float distanceX, float distanceY) {
            if (big) {
                offsetX -= distanceX;
                offsetY -= distanceY;
//                dispatchNestedPreScroll()
                int unconsumed = fixOffsets();
                if (unconsumed != 0) {
                    childHelper.dispatchNestedScroll(0, 0, 0, unconsumed, null);
                } else {
                    invalidate();
                }
            }
            return false;
        }

        @Override
        public void onLongPress(MotionEvent e) {

        }

        @Override
        public boolean onFling(MotionEvent down, MotionEvent event, float velocityX, float velocityY) {
            if (big) {
                scroller.fling((int) offsetX, (int) offsetY, (int) velocityX, (int) velocityY,
                        - (int) (bitmap.getWidth() * bigScale - getWidth()) / 2,
                        (int) (bitmap.getWidth() * bigScale - getWidth()) / 2,
                        - (int) (bitmap.getHeight() * bigScale - getHeight()) / 2,
                        (int) (bitmap.getHeight() * bigScale - getHeight()) / 2);

                postOnAnimation(henFlingRunner);
            }
            return false;
        }

        @Override
        public boolean onSingleTapConfirmed(MotionEvent e) {
            return false;
        }

        @Override
        public boolean onDoubleTap(MotionEvent e) {
            big = !big;
            if (big) {
                offsetX = (e.getX() - getWidth() / 2f) - (e.getX() - getWidth() / 2) * bigScale / smallScale;
                offsetY = (e.getY() - getHeight() / 2f) - (e.getY() - getHeight() / 2) * bigScale / smallScale;
                fixOffsets();
                getScaleAnimator().start();
            } else {
                getScaleAnimator().reverse();
            }
            return false;
        }

        @Override
        public boolean onDoubleTapEvent(MotionEvent e) {
            return false;
        }
    }

    private int fixOffsets() {
        offsetX = Math.min(offsetX, (bitmap.getWidth() * bigScale - getWidth()) / 2);
        offsetX = Math.max(offsetX, - (bitmap.getWidth() * bigScale - getWidth()) / 2);
        int result = 0;
        if (offsetY < -(bitmap.getHeight() * bigScale - getHeight()) / 2) {
            result = (int) (- (bitmap.getHeight() * bigScale - getHeight()) / 2 - offsetY);
        } else if (offsetY > (bitmap.getHeight() * bigScale - getHeight()) / 2) {
            result = (int) ((bitmap.getHeight() * bigScale - getHeight()) / 2 - offsetY);
        }
        offsetY = Math.min(offsetY, (bitmap.getHeight() * bigScale - getHeight()) / 2);
        offsetY = Math.max(offsetY, - (bitmap.getHeight() * bigScale - getHeight()) / 2);
        return result;
    }

    class HenFlingRunner implements Runnable {

        @Override
        public void run() {
            if (scroller.computeScrollOffset()) {
                offsetX = scroller.getCurrX();
                offsetY = scroller.getCurrY();
                invalidate();
                postOnAnimation(this);
            }
        }
    }

    class HenScaleListener implements ScaleGestureDetector.OnScaleGestureListener {
        float initialScale;

        @Override
        public boolean onScale(ScaleGestureDetector detector) {
            currentScale = initialScale * detector.getScaleFactor();
            invalidate();
            return false;
        }

        @Override
        public boolean onScaleBegin(ScaleGestureDetector detector) {
            initialScale = currentScale;
            return true;
        }

        @Override
        public void onScaleEnd(ScaleGestureDetector detector) {

        }
    }
}

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
//        setContentView(R.layout.drag_helper_grid_view);
//        setContentView(R.layout.drag_listener_grid_view);
//        setContentView(R.layout.drag_to_collect);
//        setContentView(R.layout.drag_up_down);
//        setContentView(R.layout.scroll_view);
//        setContentView(R.layout.nested_scroll_view);
        setContentView(R.layout.nested_scalable_image_view);

    }
}

本文地址：https://blog.csdn.net/aha_jasper/article/details/110672617