LinearLayout 的第二行中的自定义视图未显示

Question

/* Code snipet from the MainActivity */
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    /* Linear layout  */
    LinearLayout layout = (LinearLayout)findViewById(R.id.main_container);

    /* Creating two similar custom views */
    CustomView row1 = new CustomView(this);  /* First row */
    CustomView row2 = new CustomView(this);  /* second row */

    layout.add(row1,0);
    layout.add(row2,1);
}

CustomView.java

public class CustomView extends View {

    public final String TAG = "CustomView";
    Context context;

    private Drawable backgroundDrawable;

    Rect backGroundDrawableRect;

    public TextMessageView(Context context) {
        super(context);
        this.context = context;
        backgroundDrawable = ContextCompat.getDrawable(context,R.drawable.background_drawable);
    }

    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {

        super.onLayout(changed, left, top, right, bottom);

        backGroundDrawableRect.left = left;
        backGroundDrawableRect.right = right;
        backGroundDrawableRect.bottom = bottom;
        backGroundDrawableRect.top = top;

        backgroundDrawable.setBounds(backGroundDrawableRect);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        /* 100 pixel height for the view */
        setMeasuredDimension(MeasureSpec.getSize(widthMeasureSpec),100);
    }

    @Override
    protected void onDraw(Canvas canvas) {

        super.onDraw(canvas);

        if(backgroundDrawable != null) {
            backgroundDrawable.draw(canvas);
        }
    }

}

activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:id="@+id/main_container"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

</LinearLayout>

问题是在线性布局的第二行中添加的视图没有显示出来。在调试过程中，当我在开发人员选项中启用“显示布局绑定”时，我发现第二行中的视图占用了所需的空间，但没有显示可绘制的内容。

Answer 1

自定义视图的变化

   public class CustomView extends View {

   public final String TAG = "CustomView";
   Context context;

   private Drawable backgroundDrawable;

   Rect backGroundDrawableRect;

    public CustomView(Context context) {
    super(context);
    this.context = context;
    backgroundDrawable = ContextCompat.getDrawable(context,R.drawable.ic_launcher);
    }

   @Override
   protected void onLayout(boolean changed, int left, int top, int right, int bottom) {

    super.onLayout(changed, left, top, right, bottom);

 /* backGroundDrawableRect.left = left;
    backGroundDrawableRect.right = right;
    backGroundDrawableRect.bottom = bottom;
    backGroundDrawableRect.top = top;

    backgroundDrawable.setBounds(backGroundDrawableRect);
 */
    }

  @Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    /* 100 pixel height for the view */
    setMeasuredDimension(MeasureSpec.getSize(widthMeasureSpec),100);
  }

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

    if(backgroundDrawable != null) {
        backgroundDrawable.draw(canvas);
    }
   }

您的启动器活动会进行此更改

  public class Test extends Activity {

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.test1);
    /* Linear layout */
    LinearLayout layout = (LinearLayout) findViewById(R.id.main_container);

    /* Creating two similar custom views */
    CustomView row1 = new CustomView(getApplicationContext()); /* First row    */
    row1.setBackgroundColor(Color.RED);
    CustomView row2 = new CustomView(getApplicationContext()); /* Second row  */

    row2.setBackgroundColor(Color.GREEN);                           

    layout.addView(row1);
    layout.addView(row2);
  }
 }

Answer 2

Canvas 坐标会自动调整到视图的位置，因此您需要将 Drawable 的左边界和上边界设置为零：

backGroundDrawableRect.left = 0;
backGroundDrawableRect.right = right - left;
backGroundDrawableRect.bottom = bottom - top;
backGroundDrawableRect.top = 0;