如何在Canvas上绘制一个圆圈使用java for android [复制]

Question

这个问题在这里已有答案：

• How to draw circle by canvas in Android? 6个答案

我想在我的Android应用程序中在画布上画一个圆圈。我搜索了很多，并意识到我是否需要一种动态的绘画形式，可以随时更新我需要使用画布而不是imageView。

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这是我到目前为止编写的代码，但它不会在Android设备屏幕上绘制任何内容：

    private void createBitMap() {
    Bitmap bitMap = Bitmap.createBitmap(100, 100, Bitmap.Config.ARGB_8888);  //creates bmp
    bitMap = bitMap.copy(bitMap.getConfig(), true);     //lets bmp to be mutable
    Canvas canvas = new Canvas(bitMap);                 //draw a canvas in defined bmp

    Paint paint = new Paint();                          //define paint and paint color
    paint.setColor(Color.RED);
    paint.setStyle(Style.FILL_AND_STROKE);
    //paint.setAntiAlias(true);

    canvas.drawCircle(50, 50, 10, paint);
}

Answer 1

像这样更新你的createBitMap方法

private void createBitMap() {
        // Create a mutable bitmap
        Bitmap bitMap = Bitmap.createBitmap(100, 100, Bitmap.Config.ARGB_8888);

        bitMap = bitMap.copy(bitMap.getConfig(), true);
        // Construct a canvas with the specified bitmap to draw into
        Canvas canvas = new Canvas(bitMap);
        // Create a new paint with default settings.
        Paint paint = new Paint();
        // smooths out the edges of what is being drawn
        paint.setAntiAlias(true);
        // set color
        paint.setColor(Color.BLACK);
        // set style
        paint.setStyle(Paint.Style.STROKE);
        // set stroke
        paint.setStrokeWidth(4.5f);
        // draw circle with radius 30
        canvas.drawCircle(50, 50, 30, paint);
        // set on ImageView or any other view 
        imageView.setImageBitmap(bitMap);

    }

Answer 2

试试这个

创建ImageView并使用image.setImageBitmap(bitMap);使位图可见。

公共类MainActivity扩展Activity {ImageView图像;

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        image=(ImageView)findViewById(R.id.imageView1);
        createBitMap();
    }

    private void createBitMap() {
        Bitmap bitMap = Bitmap.createBitmap(100, 100, Bitmap.Config.ARGB_8888);  //creates bmp
        bitMap = bitMap.copy(bitMap.getConfig(), true);     //lets bmp to be mutable
        Canvas canvas = new Canvas(bitMap);                 //draw a canvas in defined bmp

        Paint paint = new Paint();
        // smooths
       paint.setAntiAlias(true);
        paint.setColor(Color.RED);
       paint.setStyle(Paint.Style.STROKE); 
        paint.setStrokeWidth(4.5f);
        // opacity
        //p.setAlpha(0x80); //
        canvas.drawCircle(50, 50, 30, paint);
        image.setImageBitmap(bitMap);
    }