自定义视图中的异常行为

Question

I want to make a view that it's width and height is always equal.

when user define a specfied height and width in xml, it chooses a smaller one.

for example:

    <com.mmmmar.ControlView
    android:layout_width="100dp"
    android:layout_height="200dp"
    android:background="#f00" />

it run well.

However, when I make width lager than height, It runs unexpectedly. green block is something I draw on this view, red block is the background I set in xml to indicate the area of view.

<com.mmmmar.ControlView
    android:layout_width="200dp"
    android:layout_height="100dp"
    android:background="#f00" />

here is my code

 public class ControlView extends View {

    private final static int DEFAULT_SIZE = 200;

    private int mDrawRadius;
    private Paint mPaint;

    public ControlView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    private void init() {
        // configure paint
        Paint paint = new Paint();
        paint.setAntiAlias(true);
        paint.setDither(true);
        mPaint = paint;
    }


    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        int size = dp2px(DEFAULT_SIZE, getContext());
        int width = calculateSpec(widthMeasureSpec, size);
        int height = calculateSpec(heightMeasureSpec, size);
        int radius = Math.min(width, height);
        // width should equal height.
        setMeasuredDimension(radius, radius);
        mDrawRadius = radius;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        Paint paint = mPaint;
        paint.setColor(Color.GREEN);
        paint.setStyle(Paint.Style.FILL);
        canvas.drawRect(0, 0, mDrawRadius, mDrawRadius, paint);
    }

    public int dp2px(float dp, Context context) {
        final float scale = context.getResources().getDisplayMetrics().density;
        return (int) (dp * scale + 0.5f);
    }

    public int calculateSpec(int measureSpec, int defaultSize) {
        int mode = View.MeasureSpec.getMode(measureSpec);
        int size = View.MeasureSpec.getSize(measureSpec);
        int realSize;
        if (mode == View.MeasureSpec.EXACTLY) {
            realSize = size;
        } else {
            // For Mode ：UNSPECIFIED and AT_MOST
            realSize = Math.min(size, defaultSize);
        }
        return realSize;
    }
}

Answer 1

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    int size = dp2px(DEFAULT_SIZE, getContext());
    int width = calculateSpec(widthMeasureSpec, size);
    int height = calculateSpec(heightMeasureSpec, size);
    int radius = Math.min(width, height);
    // width should equal height.
    setMeasuredDimension(radius, radius);
    mDrawRadius = radius;
}

You do not need to set measured dimension after calculating.

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    // Your logic comes here to pick smallest border
    super.onMeasure(smallest_border_that_you_pick,smallest_border_that_you_pick)
}

Would be fix your problem.