Android实现图片拖动效果

<RelativeLayoutxmlns: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">

 <ImageView

  android:id="@+id/iv_main"

  android:layout_width="wrap_content"

  android:layout_height="wrap_content"

  android:src="@drawable/test"/>

</RelativeLayout>

publicclassMainActivityextendsActivityimplementsOnTouchListener {

 privateImageView iv_main;

 privateRelativeLayout parentView;

 @Override

 protectedvoidonCreate(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);

 }

 privateintlastX;

 privateintlastY;

 privateintmaxRight;

 privateintmaxBottom;

 @Override

 publicbooleanonTouch(View v, MotionEvent event) {

  //得到事件的坐标

  inteventX = (int) event.getRawX();

  inteventY = (int) event.getRawY();

  switch(event.getAction()) {

  caseMotionEvent.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;

  caseMotionEvent.ACTION_MOVE:

   //计算事件的偏移

   intdx = eventX-lastX;

   intdy = eventY-lastY;

   //根据事件的偏移来移动imageView

   intleft = iv_main.getLeft()+dx;

   inttop = iv_main.getTop()+dy;

   intright = iv_main.getRight()+dx;

   intbottom = 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;

  }

  returntrue;//所有的motionEvent都交给imageView处理

 }

}

<?xmlversion="1.0"encoding="utf-8"?>

<LinearLayoutxmlns:Android="http://schemas.android.com/apk/res/android"

android:orientation="vertical"android:layout_width="fill_parent"

android:layout_height="fill_parent">

  <ImageViewandroid:id="@+id/imageView"android:layout_width="wrap_content"

  android:layout_height="wrap_content"

  android:layout_gravity="center_horizontal"

  android:src="@drawable/icon"/>

  <Buttonandroid:id="@+id/alpha_plus"

  android:layout_width="wrap_content"android:layout_height="wrap_content"

  android:text="透明度增加"android:layout_gravity="center_horizontal"

  />

  <Buttonandroid:id="@+id/alpha_minus"

  android:layout_width="wrap_content"android:layout_height="wrap_content"

  android:text="透明度减少"android:layout_gravity="center_horizontal"

  />

</LinearLayout>

importandroid.app.Activity;

importandroid.os.Bundle;

importandroid.os.Handler;

importandroid.view.View;

importandroid.widget.Button;

importandroid.widget.ImageView;

publicclassTOUMINGDUextendsActivity {

  privateImageView imageView=null;

  privateButton alpha_plus=null;//透明度增加

  privateButton alpha_minus=null;//透明度减少

  privateintalpha=255;//记录ImageView的透明度

  Boolean flag=true;

  @Override

    publicvoidonCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    setContentView(R.layout.main);

    imageView=(ImageView)findViewById(R.id.imageView);

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

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

    alpha_plus.setOnClickListener(listener);

    alpha_minus.setOnClickListener(listener);

  }

  privateView.OnClickListener listener =newView.OnClickListener(){

    publicvoidonClick(View v) {

      //加加

      if(v==alpha_plus){

        alpha+=10;

        if(alpha>255){

          alpha=255;

        }

        imageView.setAlpha(alpha);

      }

      //减减

      if(v==alpha_minus){

        alpha-=10;

        if(alpha<0){

          alpha=0;

        }

        imageView.setAlpha(alpha);

      }

    }

  };

}