java - 如何在 handleMessage 中使用类局部非静态变量时使 android 句柄静态

Question

此代码 fragment 在 CircleView 扩展 View 类中

private Handler handler = new Handler()
{
    @Override
    public void handleMessage(Message msg)
    {

        super.handleMessage(msg);
        if (curAng > 0 && curTime > 0) // this is non static varriable in class
        {
            curAng = curAng - (2 * Math.PI)/360;
        }
        else
        {
            curAng = 0; // this is non static variable in class
            task.cancel(); // this is non static variable in class
        }
        invalidate();
    }
};

我尝试了几个来自 stackoverflow 的解决方案，但对我没有任何作用。下面的例子

static class MyInnerHandler extends Handler{
        WeakReference<CircleView> mFrag;

        MyInnerHandler(CircleView aview) {
            mFrag = new WeakReference<CircleView>(aview);
        }

        @Override
        public void handleMessage(Message msg)
        {

            super.handleMessage(msg);
            if (curAng > 0 && curTime > 0) // this is non static variable in class
            {
                curAng = curAng - (2 * Math.PI)/360;
            }
            else
            {
                curAng = 0; // this is non static variable in class
                task.cancel(); // this is non static variable in class
            }
            invalidate();
        }
    }
    MyInnerHandler myHandler = new MyInnerHandler(this);

问题是，如果我按照上面的代码进行操作，我会收到错误消息，无法从静态上下文中引用非静态字段。我不想将私有(private)变量更改为静态变量。请帮助谢谢。(注意:- 我还在代码中的某处使用了 handler.obtainMessage().sendToTarget();)。

最后我找到了解决方案，关于如何访问类变量而不将它们设为静态。

这是答案:-

 static class MyInnerHandler extends Handler{
    WeakReference<CircleView> mFrag;

    MyInnerHandler(CircleView aview) {
        mFrag = new WeakReference<CircleView>(aview);
    }

    @Override
    public void handleMessage(Message msg)
    {
        CircleView aview = mFrag.get(); // Here is solution. with aview. can access all method and variables.  
        super.handleMessage(msg);
        if (aview.curAng > 0 && aview.curTime > 0) // this is non static varriable in class
        {
            aview.curAng = curAng - (2 * Math.PI)/360;
        }
        else
        {
            aview.curAng = 0; // this is non static variable in class
            aview.task.cancel(); // this is non static variable in class
        }
        aview.invalidate();
    }
}
MyInnerHandler myHandler = new MyInnerHandler(this);

Answer 1

我认为除了像您那样做之外，您最好在继续之前检查 aview 是否为空。因为当消息被发布到处理程序时，原始 View 可能已经消失并且有机会已经被垃圾收集。

@Override
 public void handleMessage(Message msg)
 {

    super.handleMessage(msg);

    CircleView aview = mFrag.get(); // Here is solution. 
                    //with aview. can access all method and variables.  


    if (aview==null) return;

     ... ...
}