Android：在运行时更改矩形的颜色

问题描述：

我有一个 LinearLayout 并且有一个自定义视图：

I have a LinearLayout and I have a custom view:

public class myView extends View  
{
    Rect rects = new Rect(30,30,80,80); 
    Canvas myCanvas;
    @Override
    public void onDraw(Canvas canvas)     
    {
         myCanvas = canvas;
         paint.setColor(Color.RED);
         canvas.drawRect(rects, paint);

    }
    void changeColor()
    {
        paint.setColor(Color.BLUE);
        myCanvas.drawRect(rects, paint);
        myCanvas.invalidate();
    }
}

在MainActiviy中，我有：

in MainActiviy I have:

LinearLayout lv = (LinearLayout) View.inflate(this, R.layout.activity_main, null);
drawView = new myView(this);
lv.addView(drawView); 
setContentView(lv);
Button button3 = (Button) findViewById(R.id.button3);
button3.setOnClickListener(new View.OnClickListener()
{
        @Override
        public void onClick(View v) {
            drawView.changeColor();
        }  
});

单击按钮后，我想通过调用changeColor更改矩形的颜色。但是在其他地方创建了新矩形！你能帮我吗？

After clicking a button I want to change the color of rectangle by calling changeColor. But new rectangle in some other place is created! Can you please help me?

答

您正在呼叫 drawRect 两次（在使视图无效之前，以及在 onDraw 上）。另外，也无需存储对 Canvas 的引用。

You're calling to drawRect twice (before invalidating the view, and on onDraw). Also, there's no need to store a reference to Canvas.

将所需的颜色保留在变量中，对其进行更改并使视图无效。-

Keep the desired color in a variable, change it and invalidate the view.-

public class myView extends View {

    private Color color = Color.RED;

    Rect rects = new Rect(30,30,80,80); 

    @Override
    public void onDraw(Canvas canvas) {
         paint.setColor(color);
         canvas.drawRect(rects, paint);
    }

    void changeColor() {
        color = Color.BLUE
        invalidate();
    }
}

Android：在运行时更改矩形的颜色

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