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我创建了一个自定义视图来在屏幕上画一条线。onCreateView此视图包含在片段的 xml 布局中，并在片段的方法中检索如下：

MyCustomView mMyCustomView;

public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    // Inflate view
    View v = inflater.inflate(R.layout.fragment, container, false);

    mMyCustomView = (MyCustomView) v.findViewById(R.id.my_custom_view);
    ...
}

当我将mMyCustomView变量传递给片段onCreateView方法中的自定义侦听器并在侦听器类中调用类似的东西mMyCustomView.drawLine时，一切正常。

然而，当我调用mMyCustomView.drawLine片段的onResume()方法时，没有任何反应，尽管它是相同的变量和方法。

我能想到的唯一原因是，当用户与片段交互时，侦听器调用该方法，onResume()就生命周期而言，这甚至比被调用的还要晚。但是，在片段中，我不能在onResume()AFAIK 之后调用该方法。

编辑 1：

这是我的自定义视图的样子：

public class ConnectionLinesView extends View {
// Class variables
Paint mPaint = new Paint(); // Paint to apply to lines
ArrayList<float[]> mLines = new ArrayList<float[]>(); // Array to store the lines


public ConnectionLinesView(Context context) {
    super(context);

    mPaint.setColor(Color.BLACK);
    mPaint.setStrokeWidth(2);
}


public ConnectionLinesView(Context context, AttributeSet attrs) { 
    super(context, attrs);

    mPaint.setColor(Color.BLACK);
    mPaint.setStrokeWidth(2);
}


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

    mPaint.setColor(Color.BLACK);
    mPaint.setStrokeWidth(2);
}


protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    // If lines were already added, draw them
    if(!mLines.isEmpty()){
        for(float[] line : mLines){
            canvas.drawLine(line[0], line[1], line[2], line[3], mPaint);
        }
    }

}


// Method to add a line to the view
public void addLine(View v1, View v2) {
    float[] line = new float[4];
    line[0] = v1.getX() + v1.getWidth()/2;
    line[1] = v1.getY() + v1.getHeight()/2;
    line[2] = v2.getX() + v2.getWidth()/2;
    line[3] = v2.getY() + v2.getHeight()/2;

    mLines.add(line);
    this.invalidate();
}


public void removeLines() {
    mLines.clear();
    this.invalidate();
}

}

当我调用 addLine(...) inonResume()时，即使onDraw()到达方法中 for 循环的内部，也不会绘制线。当我稍后在侦听器类（响应某些用户交互）中添加另一条线时，两条线都绘制在画布上。不知何故，在视图的父片段中 canvas.drawLine()不起作用。onResume()

编辑 2：

I have added a handler, that calls the custom view's invalidate method repeatedly after the fragment has been added to the layout of the parent activity. The line still doesn't get drawn!

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1 回答 1

3

In the end I solved the problem by creating a handler, which calls the addLine method after 50 milliseconds after the fragment has been added. A pretty dirty solution, but it works...

于 2012-04-25T11:29:27.387 回答