Android——控件跟随手指移动

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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; @Overrideprotected 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);  }@Overridepublic 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;}@Overridepublic 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>