創建自定義視圖和XML命名空間

Question

我試圖在Android的我提到在MainActivity我所有的arrtrs名單和XML文件自定義的意見，但我有在main.xml錯誤：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:tools="http://schemas.android.com/tools" 
    xmlns:custom="http://schemas.android.com/apk/res/com.example.customviews.piechart" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:orientation="vertical"> 

    <com.example.customviews.charting.piechart.MainActivity 
     android:layout_width="match_parent" 
     android:layout_height="?android:attr/listPreferredItemHeight" 
     custom:titleText="Background color" 
     custom:valueColor="@android:color/holo_green_light" 
     /> 

</LinearLayout> 

Answer 1

你有一個沒有參數的構造函數？

像您應該添加一個構造函數：

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

或

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

你問一個自定義視圖的一個簡單的例子：

public class BirdView extends ImageView { 

private float direction = 0; 
Paint paint = new Paint(); 

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

public BirdView(Context context, AttributeSet attrs) { 
    super(context, attrs); 
    paint.setColor(Color.WHITE); 
    paint.setStrokeWidth(6); 
} 

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

@Override 
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { 
    setMeasuredDimension(MeasureSpec.getSize(widthMeasureSpec), 
      MeasureSpec.getSize(heightMeasureSpec)); 
} 

@Override 
public void draw(Canvas canvas) { 
    canvas.save(); 
    int stratX = getWidth()/2; 
    int startY = getHeight()/2; 
    canvas.rotate(direction, stratX, startY); 
    super.draw(canvas); 
    canvas.restore(); 
    canvas.drawLine(stratX, startY, stratX, startY + 80, paint); 
} 

public void update(float dir) { 
    direction = dir; 
    invalidate(); 
} 

}