android 画布可以拖动,Android控件拖动实例详解

Android控件拖动

Android控件的拖动，主要是通过设置控件的setOnTouchListener()方法，重写它的onTouch()方法。然后通过MotionEvent的不同事件，进行判断，主要是在MotionEvent.ACTION_MOVE中不断重绘控件在画布中的位置，而实现拖动的效果。

public class DragViewActivity extends AppCompatActivity {

private Button btn_drag;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_drag_view);

// 获取屏幕的宽高

DisplayMetrics dm = getResources().getDisplayMetrics();

final int screenWith = dm.widthPixels;

final int screenHeight = dm.heightPixels;

btn_drag = (Button) findViewById(R.id.btn_drag);

btn_drag.setOnTouchListener(new View.OnTouchListener() {

int lastX;

int lastY;

boolean isDraging = false;

@Override

public boolean onTouch(View v, MotionEvent event) {

int ee = event.getAction();

switch (ee){

case MotionEvent.ACTION_DOWN:

isDraging = true;

lastX = (int) event.getRawX();

lastY = (int) event.getRawY();

break;

case MotionEvent.ACTION_MOVE:

if (isDraging){

// x轴方向的位移差

int dx = (int) event.getRawX() - lastX;

// y轴方向的位移差

int dy = (int) event.getRawY() - lastY;

int l = v.getLeft() + dx;

int t = v.getTop() + dy;

int r = v.getRight() + dx;

int b = v.getBottom() + dy;

// 判断超出屏幕

if (l < 0){

l = 0;

r = l + v.getWidth();

}

if (t < 0){

t = 0;

b = t + v.getHeight();

}

if (r > screenWith){

r = screenWith;

l = r - v.getWidth();

}

if (b > screenHeight){

b = screenHeight;

t = b - v.getHeight();

}

// 重绘view

v.layout(l, t, r, b);

v.postInvalidate();

lastX = (int) event.getRawX();

lastY = (int) event.getRawY();

}

break;

case MotionEvent.ACTION_UP:

isDraging = false;

break;

default:

break;

}

return false;

}

});

}

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