android两种方式中自己画一个圆，实现单点触控时拖动图片，跟着拖动点走，并且可以放大或缩小

MainActivity类

public class MainActivity extends Activity {

    View view;
    public static final int DRAG = 1;
    public static final int SCALE = 2;
    int mode = 1;

    int height = 10, width = 10;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        getWindow().requestFeature(Window.FEATURE_NO_TITLE);
        setContentView(R.layout.activity_main);
        view = findViewById(R.id.view);
    }

    float length = 1;

    // 重写
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int x = (int) event.getX();
        int y = (int) event.getY();
        // 多指触控
        switch (event.getAction() & event.getActionMasked()) {
        case MotionEvent.ACTION_DOWN:
            mode = DRAG;
            break;
        case MotionEvent.ACTION_POINTER_DOWN:
            Log.e("TAG", "多指移动");
            mode = SCALE;
            // 两个手指开始的长度是多少呢？
            length = calc(event);
            break;
        case MotionEvent.ACTION_UP:
            length = 1;
            break;
        case MotionEvent.ACTION_MOVE:
            if (mode == DRAG) {
                // 1. 单个手指
                FrameLayout.LayoutParams params = new FrameLayout.LayoutParams(
                        width, height);
                params.setMargins(x, y, 0, 0);
                view.setLayoutParams(params);
            } else {
                // 2. 两个手指
                float beilv = calc(event) / length;
                width = (int) (view.getWidth() * beilv);
                height = (int) (view.getHeight() * beilv);
                Log.e("TAG", beilv + "  " + width + "  " + height);

                FrameLayout.LayoutParams params = (LayoutParams) view
                        .getLayoutParams();
                params.width = width;
                params.height = height;
                view.setLayoutParams(params);
            }
            break;
        }
        return true;
    }

    // 类 Ponint
    public float calc(MotionEvent event) {
        float x1 = event.getX();
        float y1 = event.getY();
        float x2 = event.getX(1);
        float y2 = event.getY(1);
        return (float) Math.sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
    }
}

xml类

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.lesson6_work1.MainActivity" >

    <View
        android:id="@+id/view"
        android:layout_width="10dp"
        android:layout_height="10dp"
        android:background="@drawable/oval" />

FrameLayout>

自己在shape中定义的一个圆的oval.xml

<shape xmlns:android="http://schemas.android.com/apk/res/android" android:shape="oval">

    <solid android:color="@android:color/holo_red_dark"/>

shape>

用自定义View的方式实现单点触控时拖动图片，跟着拖动点走

QiuView 类

public class QiuView extends View {

    Paint paint = new Paint();


    PointF point = new PointF();

    public QiuView(Context context) {
        super(context);
        paint.setColor(Color.RED);
        paint.setAntiAlias(true);
        paint.setDither(true);
    }


    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawCircle(point.x, point.y, 50, paint);
    }


    //   触摸事件
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        if (event.getAction() == MotionEvent.ACTION_MOVE) {
            point.set(event.getX(), event.getY());
            invalidate();
        }
        return true;
    }
}

MainActivity 类

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(new QiuView(this));

    }
}