自定义View典型写法

自定义View

继承View或者现有控件, 根据需求加入自己的逻辑

使用自定义View

xml中使用全路径名

自定义属性

res/value目录创建 attrs.xml
    <declare-styleable/>
        创建自定义属性
            <attr name format/>
创建的属性可以在自定义View里面引用             

使用自定义属性

    添加app命名空间
        xmlns:app="http://schemas.android.com/apk/res-auto"

        以app开头使用自定义属性

java代码中获取自定义属性

TypedArray typedArray = context.obtainStyledAttributes

TypedArray可以使用很多getXXX()方法获取到自定义属性的值
用完记得typedArray.recycle();

支持wrap_content

判断宽/高测量模式, 是MeasureSpec.AT_MOST就设置默认宽高

支持padding

onDraw中计算padding

示例:

attrs.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="CircleView">
        <attr name="circle_color" format="color|reference" />
    </declare-styleable>
</resources>

CircleView.java

public class CircleView extends View {
    public static final int DEFAULT_WIDTH = 200;
    public static final int DEFAULT_HEIGHT = 200;
    private int mColor = Color.RED;
    private Paint mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);

    public CircleView(Context context) {
        this(context, null);
    }

    public CircleView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public CircleView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.CircleView);
        mColor = typedArray.getColor(R.styleable.CircleView_circle_color, Color.RED);
            typedArray.recycle();
        init();
    }

    private void init() {
        mPaint.setColor(mColor);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        int widthSpecMode = MeasureSpec.getMode(widthMeasureSpec);
        int widthSpecSize = MeasureSpec.getSize(widthMeasureSpec);
        int heightSpecMode = MeasureSpec.getMode(heightMeasureSpec);
        int heightSpecSize = MeasureSpec.getSize(heightMeasureSpec);

        if (widthSpecMode == MeasureSpec.AT_MOST && widthSpecMode == MeasureSpec.AT_MOST) {
            setMeasuredDimension(dp2px(DEFAULT_WIDTH), dp2px(DEFAULT_HEIGHT));
        } else if (widthSpecMode == MeasureSpec.AT_MOST) {
            setMeasuredDimension(dp2px(DEFAULT_WIDTH), heightSpecSize);
        } else if (heightSpecMode == MeasureSpec.AT_MOST) {
            setMeasuredDimension(widthSpecSize, dp2px(DEFAULT_HEIGHT));
        }
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        int paddingLeft = getPaddingLeft();
        int paddingRight = getPaddingRight();
        int paddingTop = getPaddingTop();
        int paddingBottom = getPaddingBottom();

        int width = getWidth() - paddingLeft - paddingRight;
        int height = getHeight() - paddingTop - paddingBottom;
        int radius = Math.min(width, height) / 2;
        canvas.drawCircle(paddingLeft + width / 2, paddingTop + height / 2, radius, mPaint);
    }

    public int dp2px(float dpValue) {
        final float scale = getContext().getResources().getDisplayMetrics().density;
        return (int) (dpValue * scale + 0.5f);
    }
}