要求:
1.通过手指移动来拖动图片
2.控制图片不能超出屏幕显示区域
技术点:
1.MotionEvent处理
2.对View进行动态定位(layout)
activity_main.xml:
MainActivity:
public class MainActivity extends Activity implements OnTouchListener { private ImageView iv_main; private RelativeLayout parentView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); iv_main = (ImageView) findViewById(R.id.iv_main); parentView = (RelativeLayout) iv_main.getParent(); /* int right = parentView.getRight(); //0 int bottom = parentView.getBottom(); //0 Toast.makeText(this, right+"---"+bottom, 1).show(); */ //设置touch监听 iv_main.setOnTouchListener(this); } private int lastX; private int lastY; private int maxRight; private int maxBottom; @Override public boolean onTouch(View v, MotionEvent event) { //得到事件的坐标 int eventX = (int) event.getRawX(); int eventY = (int) event.getRawY(); switch (event.getAction()) { case MotionEvent.ACTION_DOWN: //得到父视图的right/bottom if(maxRight==0) {//保证只赋一次值 maxRight = parentView.getRight(); maxBottom = parentView.getBottom(); } //第一次记录lastX/lastY lastX =eventX; lastY = eventY; break; case MotionEvent.ACTION_MOVE: //计算事件的偏移 int dx = eventX-lastX; int dy = eventY-lastY; //根据事件的偏移来移动imageView int left = iv_main.getLeft()+dx; int top = iv_main.getTop()+dy; int right = iv_main.getRight()+dx; int bottom = iv_main.getBottom()+dy; //限制left >=0 if(left<0) { right += -left; left = 0; } //限制top if(top<0) { bottom += -top; top = 0; } //限制right <=maxRight if(right>maxRight) { left -= right-maxRight; right = maxRight; } //限制bottom <=maxBottom if(bottom>maxBottom) { top -= bottom-maxBottom; bottom = maxBottom; } iv_main.layout(left, top, right, bottom); //再次记录lastX/lastY lastX = eventX; lastY = eventY; break; default: break; } return true;//所有的motionEvent都交给imageView处理 } }
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