ValueAnimator自定义控件实现动画打开关闭效果。

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:layout_width="match_parent"
              android:layout_height="match_parent"
              android:background="@android:color/white"
              android:divider="@drawable/divider"
              android:orientation="vertical"
              android:showDividers="middle">

    <LinearLayout
        android:id="@+id/ll_expanded_question"
        android:layout_width="match_parent"
        android:layout_height="48dp"
        android:gravity="center_vertical">

        <TextView
            android:id="@+id/tv_expanded_question"
            android:layout_width="0dp"
            android:layout_height="48dp"
            android:layout_weight="1"
            android:gravity="center_vertical"
            android:padding="8dp"
            android:text="如何把一本很难的书看懂？"
            android:textColor="#999999"
            android:textSize="16sp"/>

        <ImageView
            android:id="@+id/iv_expanded_indicator"
            android:layout_width="16dp"
            android:layout_height="16dp"
            android:layout_marginRight="16dp"
            android:src="@drawable/img_up"/>

    </LinearLayout>


    <TextView
        android:id="@+id/tv_expanded_answer"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="8dp"
        android:text="多读几遍。真的特别有用。至少看三遍。从开头看，看到中间，重头再来，再看得多一点，在从新开始，建议看到快结束时再从新开始。"
        android:textColor="#999999"
        android:textSize="16sp"/>
</LinearLayout>

public class ExpandedView extends FrameLayout {

    private TextView mTvAnswer;
    private boolean isClosed;
    private ImageView mIvIndicator;

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

    private void init(Context context) {
        View view = LayoutInflater.from(context).inflate(R.layout.expanded_view, this, true);
        LinearLayout llQuestion = (LinearLayout) view.findViewById(R.id.ll_expanded_question);
        llQuestion.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                anim();
            }
        });
        mTvAnswer = (TextView) view.findViewById(R.id.tv_expanded_answer);
        mIvIndicator = (ImageView) view.findViewById(R.id.iv_expanded_indicator);
    }

    private void anim() {
        // 指示器旋转
        ValueAnimator valueAnimator1 = isClosed
                ? ValueAnimator.ofFloat(180, 0)
                : ValueAnimator.ofFloat(0, 180);
        valueAnimator1.setDuration(500);
        valueAnimator1.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator animation) {
                float value = (float) animation.getAnimatedValue();
                mIvIndicator.setRotation(value);
            }
        });
        valueAnimator1.start();

        // 打开开关闭操作
        final int answerHeight = mTvAnswer.getMeasuredHeight();
        ValueAnimator valueAnimator2 = isClosed
                ? ValueAnimator.ofInt(-answerHeight, 0)
                : ValueAnimator.ofInt(0, -answerHeight);
        valueAnimator2.setDuration(500);
        final MarginLayoutParams params = (MarginLayoutParams) mTvAnswer.getLayoutParams();
        valueAnimator2.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator animation) {
                int value = (int) animation.getAnimatedValue();
                params.bottomMargin = value;
                mTvAnswer.setLayoutParams(params);
            }
        });
        valueAnimator2.addListener(new Animator.AnimatorListener() {
            @Override
            public void onAnimationStart(Animator animation) {

            }

            @Override
            public void onAnimationEnd(Animator animation) {
                isClosed = !isClosed;
            }

            @Override
            public void onAnimationCancel(Animator animation) {

            }

            @Override
            public void onAnimationRepeat(Animator animation) {

            }
        });
        valueAnimator2.start();
    }
}

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