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

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>