Android开发中遇到过的坑——控件跟随手指移动

思路

实现任意控件跟随手指触摸移动。核心思路监听onTouch事件，在ACTION_MOVE中改变控件的坐标。思路虽然简单，但其中还有一些坑。
本文的思路借鉴了http://blog.csdn.net/actual_/article/details/8582313这位博主的代码，但他的代码有个Bug，即当拖动控件到屏幕中间位置时控件会变形，分析其代码，主要问题出现在：

case MotionEvent.ACTION_MOVE:              RelativeLayout.LayoutParams layoutParams =    (RelativeLayout.LayoutParams) view                      .getLayoutParams();              layoutParams.leftMargin = X - _xDelta;              layoutParams.topMargin = Y - _yDelta;              layoutParams.rightMargin = -250;              layoutParams.bottomMargin = -250;              view.setLayoutParams(layoutParams);              break;

其中设置了控件上、下、左、右元素间隔的距离，从而完成在RelativeLayout布局中对于控件位置的设置，但是当左右间隔或上下间隔之和不对的时候，则会挤压控件的长宽。

这里换一个思路，其实只设置控件距上、左元素的距离即可完成RelativeLayout布局中控件位置的设置，并设置控件的长宽，保持其形状大小不变。

case MotionEvent.ACTION_MOVE:                  int dx = (int) event.getRawX() - lastX;                int dy = (int) event.getRawY() - lastY;                int left = view.getLeft() + dx;                int top = view.getTop() + dy;                RelativeLayout.LayoutParams layoutParams = (RelativeLayout.LayoutParams) view                         .getLayoutParams();                  layoutParams.height=IMAGE_SIZE;                layoutParams.width = IMAGE_SIZE;                layoutParams.leftMargin =left;                  layoutParams.topMargin =top;                  view.setLayoutParams(layoutParams);                lastX = (int) event.getRawX();                lastY = (int) event.getRawY();                break;

主要代码

MainActivity.java

import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.Menu;import android.view.MenuItem;import android.view.MotionEvent;import android.view.View;import android.view.View.OnTouchListener;import android.view.ViewGroup;import android.widget.Button;import android.widget.ImageView;import android.widget.RelativeLayout;public class MainActivity extends AppCompatActivity implements OnTouchListener {    ImageView _view,_view2;      ViewGroup _root;      private int lastX, lastY;    final static int IMAGE_SIZE = 72;     @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        _root = (ViewGroup) findViewById(R.id.root);          _view = (ImageView) findViewById(R.id.id_text);          _view2 = (ImageView) findViewById(R.id.id_text2);         RelativeLayout.LayoutParams layoutParams = new RelativeLayout.LayoutParams(                  IMAGE_SIZE, IMAGE_SIZE);          layoutParams.leftMargin = IMAGE_SIZE;          layoutParams.topMargin = IMAGE_SIZE;          _view.setLayoutParams(layoutParams);          _view.setOnTouchListener(this);         RelativeLayout.LayoutParams layoutParams2 = new RelativeLayout.LayoutParams(                  IMAGE_SIZE, IMAGE_SIZE);          layoutParams2.leftMargin = 3*IMAGE_SIZE;          layoutParams2.topMargin = IMAGE_SIZE;          _view2.setLayoutParams(layoutParams2);          _view2.setOnTouchListener(this);      }    @Override    public boolean onCreateOptionsMenu(Menu menu) {        // Inflate the menu; this adds items to the action bar if it is present.        getMenuInflater().inflate(R.menu.main, menu);        return true;    }    @Override    public boolean onOptionsItemSelected(MenuItem item) {        // Handle action bar item clicks here. The action bar will        // automatically handle clicks on the Home/Up button, so long        // as you specify a parent activity in AndroidManifest.xml.        int id = item.getItemId();        if (id == R.id.action_settings) {            return true;        }        return super.onOptionsItemSelected(item);    }     public boolean onTouch(View view, MotionEvent event) {              final int X = (int) event.getRawX();              final int Y = (int) event.getRawY();              switch (event.getAction() & MotionEvent.ACTION_MASK) {              case MotionEvent.ACTION_DOWN:                  lastX = (int) event.getRawX();                lastY = (int) event.getRawY();                RelativeLayout.LayoutParams lParams = (RelativeLayout.LayoutParams) view                          .getLayoutParams();                   break;              case MotionEvent.ACTION_UP:                  break;              case MotionEvent.ACTION_POINTER_DOWN:                  break;              case MotionEvent.ACTION_POINTER_UP:                  break;              case MotionEvent.ACTION_MOVE:                  int dx = (int) event.getRawX() - lastX;                int dy = (int) event.getRawY() - lastY;                int left = view.getLeft() + dx;                int top = view.getTop() + dy;                RelativeLayout.LayoutParams layoutParams = (RelativeLayout.LayoutParams) view                         .getLayoutParams();                  layoutParams.height=IMAGE_SIZE;                layoutParams.width = IMAGE_SIZE;                layoutParams.leftMargin =left;                  layoutParams.topMargin =top;                  view.setLayoutParams(layoutParams);                lastX = (int) event.getRawX();                lastY = (int) event.getRawY();                break;              }              _root.invalidate();              return true;          }  }

activity_main.xml

这里写代码片<RelativeLayout 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"      android:id="@+id/root"      tools:context=".MainActivity" >      <ImageView          android:id="@+id/id_text"          android:layout_width="wrap_content"          android:layout_height="wrap_content"          android:layout_centerHorizontal="true"          android:layout_centerVertical="true"          android:background="@drawable/pin2"         />     <ImageView          android:id="@+id/id_text2"          android:layout_width="wrap_content"          android:layout_height="wrap_content"          android:layout_centerHorizontal="true"          android:layout_centerVertical="true"          android:background="@drawable/pin2"        /> RelativeLayout>

Android——控件跟随手指移动

Android开发中遇到过的坑——控件跟随手指移动

思路

主要代码

MainActivity.java

activity_main.xml

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