自定义View绘制圆，可拖动

来源：互联网发布：唐璜歌剧经典曲目知乎编辑：程序博客网时间：2024/05/16 14:00

### 新建类CustomView 继承View

### main布局

<com.example.myapplication_view.CustomView    android:layout_width="wrap_content"    android:layout_height="wrap_content" />

### MainActivity

public class MainActivity extends AppCompatActivity {    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        //一个参数的构造方法调用//        CustomView view  = new CustomView(this);//         setContentView(view);        setContentView(R.layout.activity_main);//两个参数的构造方法调用    }}

### CustomView类

public class CustomView extends View {    private static final int WIDTH = 90;    private Rect rect = new Rect(0, 0, WIDTH, WIDTH);//绘制矩形的区域    private int deltaX,deltaY;//点击位置和图形边界的偏移量//    private int moveX,moveY;    private static Paint paint = new Paint();//画笔    public CustomView(Context context) {        super(context);        paint = new Paint();        paint.setColor(Color.BLUE);//填充蓝色        paint.setAntiAlias(true);    }    public CustomView(Context context, AttributeSet attrs) {        super(context, attrs);        paint = new Paint();        paint.setColor(Color.RED);//填充红色        paint.setAntiAlias(true);    }    @Override    protected void onDraw(Canvas canvas) {        super.onDraw(canvas);        canvas.drawCircle(rect.centerX(),rect.centerY(),WIDTH/2, paint);//画矩形    }    @Override    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {        super.onMeasure(widthMeasureSpec, heightMeasureSpec);    }    @Override    public boolean onTouchEvent (MotionEvent event) {        int x = (int) event.getX();        int y = (int) event.getY();        switch(event.getAction()) {            case MotionEvent.ACTION_DOWN:                if(!rect.contains(x, y)) {                    return false;//没有在矩形上点击，不处理触摸消息                }                deltaX = x - rect.left;                deltaY = y - rect.top;                break;            case MotionEvent.ACTION_MOVE:            case MotionEvent.ACTION_UP:                Rect old = new Rect(rect);//                更新矩形的位置                rect.left = x - deltaX;                rect.top = y - deltaY;                rect.right = rect.left + WIDTH;                rect.bottom = rect.top + WIDTH;                old.union(rect);//要刷新的区域，求新矩形区域与旧矩形区域的并集                invalidate(old);//出于效率考虑，设定脏区域，只进行局部刷新，不是刷新整个view                break;        }        return true;//处理了触摸消息，消息不再传递    }}

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