可以在视图绘制之前调用setClipBounds吗？

Question

我正在构建一个自定义复合控件.该复合控件的一个组件是自定义按钮.我的ShiftingTabButton是我的复合控件类中的嵌套类.

我需要将ShiftingTabButton的clipBounds设置为略短于首次绘制时的实际高度.

在下面显示的ShiftingTabButton构造函数中,我设置了一些必要的参数,然后measure()使用mode 调用UNSPECIFIED,以确定新视图的预期大小.当我在调试模式下运行时,我可以看到width= 160和height= 64我的Nexus 7.

到目前为止都很好.

但是当我尝试使用修改后的clipBounds调用setClipBounds()时,应用程序崩溃了.

我已经尝试useShorterClipBounds在构造函数中定义一个标志,将方法的设置移动clipBounds到onDraw()方法并使其依赖于标志检查,但我仍然得到同样的崩溃.

public ShiftingTabButton(Context context, String string) {
    super(context);

    // parameter setup
    this.setText(string);
    this.setBackground(getResources().getDrawable(R.drawable.tab_unselected));
    this.setId(generateChildViewId());
    this.setTextSize(TypedValue.COMPLEX_UNIT_SP, 14);
    this.setPadding(dpToPx(7), 0, dpToPx(7), 0);

    // measure the view     
    int widthMeasureSpec = MeasureSpec.makeMeasureSpec(ViewGroup.LayoutParams.WRAP_CONTENT, MeasureSpec.UNSPECIFIED);
    int heightMeasureSpec = MeasureSpec.makeMeasureSpec(ViewGroup.LayoutParams.WRAP_CONTENT, MeasureSpec.UNSPECIFIED);
    this.measure(widthMeasureSpec, heightMeasureSpec);
    int width = this.getMeasuredWidth();
    int height = this.getMeasuredHeight();

    // adjust the clipBounds        
    Rect clipBounds = new Rect();
    clipBounds.set(0, 0, width, height - dpToPx(16));
    this.setClipBounds(clipBounds); // !App crashes executing this line of code!
}

Answer 1

您可以轻松地复制实现以支持旧版本:

private Rect mClipBounds;

@Override
public void draw(Canvas canvas) {
    // Clip bounds implementation for JB_MR1 and older
    // Does not save the canvas, because the View implementation also doesn't...
    if (mClipBounds != null) {
        canvas.clipRect(mClipBounds);
    }
    super.draw(canvas);
}

@Override
@TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR2)
public void setClipBounds(Rect clipBounds) {
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR2) {
        super.setClipBounds(clipBounds);
        return;
    }

    if (clipBounds != null) {
        if (clipBounds.equals(mClipBounds)) {
            return;
        }
        if (mClipBounds == null) {
            invalidate();
            mClipBounds = new Rect(clipBounds);
        } else {
            invalidate(Math.min(mClipBounds.left, clipBounds.left),
                    Math.min(mClipBounds.top, clipBounds.top),
                    Math.max(mClipBounds.right, clipBounds.right),
                    Math.max(mClipBounds.bottom, clipBounds.bottom));
            mClipBounds.set(clipBounds);
        }
    } else {
        if (mClipBounds != null) {
            invalidate();
            mClipBounds = null;
        }
    }
}

@Override
@TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR2)
public Rect getClipBounds() {
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR2) {
        return super.getClipBounds();
    } else {
        return (mClipBounds != null) ? new Rect(mClipBounds) : null;
    }
}