android - 难以创建我自己的自定义 View

Question

所以我试图在 xml 布局之外创建自己的 View ，但很难让它显示任何内容。我确定我遗漏了一些简单的东西，但看不到它可能是什么。任何输入表示赞赏。这是我用于测试目的的两个类。

public class TestSuite extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // Turns off the application title at the top..
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        // Turns off the status bar at the top..
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);

        setContentView(new Background(this));
    }
}

和

public class Background extends View {

    public Background(Context context) {
        super(context);
    }

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

    public Background(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

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

        Resources res = getResources();

        Rect baseRectBounds = new Rect(0,0,200,200);
        Rect topRectBounds = new Rect(20,20,160,160);
        Rect bottomRectBounds = new Rect(40,40,120,120);

        Paint baseColor = new Paint(res.getColor(R.color.blue));
        Paint topColor = new Paint(res.getColor(R.color.red));
        Paint bottomColor = new Paint(res.getColor(R.color.green));

        canvas.drawRect(baseRectBounds, baseColor);
        canvas.drawRect(topRectBounds, topColor);
        canvas.drawRect(bottomRectBounds, bottomColor);
    }

}

编辑

这是我正在使用的最新 onDraw 方法。

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

    Resources res = getResources();

    Rect canvasBounds = canvas.getClipBounds();

    Log.v("CanvasBounds before", "left - " + canvasBounds.left);
    Log.v("CanvasBounds before", "top - " + canvasBounds.top);
    Log.v("CanvasBounds before", "right - " + canvasBounds.right);
    Log.v("CanvasBounds before", "bottom - " + canvasBounds.bottom);

    Rect baseRect = new Rect(0,0,200,200);
    Rect topRect = new Rect(20,20,160,160);
    Rect botRect = new Rect(40,40,120,120);

    Paint baseColor = new Paint(res.getColor(R.color.red)); 
    Paint topColor = new Paint(res.getColor(R.color.green));
    Paint botColor = new Paint(res.getColor(R.color.blue));
    baseColor.setStyle(Style.FILL);
    topColor.setStyle(Style.FILL);
    botColor.setStyle(Style.FILL);

    canvas.drawRect(baseRect, baseColor);
    canvas.drawRect(topRect, topColor);
    canvas.drawRect(botRect, botColor);

    canvasBounds = canvas.getClipBounds();

    Log.v("CanvasBounds after", "left - " + canvasBounds.left);
    Log.v("CanvasBounds after", "top - " + canvasBounds.top);
    Log.v("CanvasBounds after", "right - " + canvasBounds.right);
    Log.v("CanvasBounds after", "bottom - " + canvasBounds.bottom);
}

Log语句的结果如下:

CanvasBounds before left - 0
CanvasBounds before top - 0
CanvasBounds before right - 480
CanvasBounds before bottom - 800
CanvasBounds after  left - 0
CanvasBounds after  top - 0
CanvasBounds after  right - 480
CanvasBounds after  bottom - 800

完成编辑

感谢 Ted 的帮助，这是我最后的 onDraw 方法(对于可能需要它的其他人)。

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

    Resources res = getResources();

    Rect baseRect = new Rect(0,0,200,200);
    Rect topRect = new Rect(20,20,160,160);
    Rect botRect = new Rect(40,40,120,120);

    Paint color = new Paint();

    color.setColor(res.getColor(R.color.red));
    canvas.drawRect(baseRect, color);
    color.setColor(res.getColor(R.color.blue));
    canvas.drawRect(topRect, color);
    color.setColor(res.getColor(R.color.green));
    canvas.drawRect(botRect, color);
}

Answer 1

两个建议:

1. 在你的c'tor中，调用setLayoutParams(new LayoutParams(FILL_PARENT, FILL_PARENT))(这里，LayoutParams是ViewGroup.LayoutParams)
2. 覆盖measure(int,int) 并按照docs for View 中的建议实现它