android手把手教你开发launcher（三）

1. 监听GridView的onItemClick事件
设置一个监听器是为了当gridView的某项被点击时，会有一个回调函数通知我们。
我们调用appsGrid.setOnItemClickListener(listener); 设置一个监听器
appsGrid.setOnItemClickListener(listener)中的listener是一个接口，其类型为：android.widget.AdapterView.OnItemClickListener
 
下面我们new一个android.widget.AdapterView.OnItemClickListener类型的对象作为参数。我们直接使用eclipde的自动补全功能来完成OnItemClickListener 的定义：

 private OnItemClickListener listener = new OnItemClickListener() {
         @Override
         public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {

         }
     }

接口OnItemClickListener 中有一个方法叫做onItemClick，我们实现它即可。下面我对onItemClick的几个参数略作说明：
parent     略
view          被点击的view
position     被点击项的位置
id             被点击项的id

2.启动被点击应用的activity

一般来讲，我们根据position即可知道被点击的项目是哪一项了。现在我们根据被点击的项目，取出对应的应用程序数据（主要是其中的主activity），然后启动activity。用下面代码实现：

?

 private OnItemClickListener clickListener = new OnItemClickListener() {
         @Override
         public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
             ResolveInfo info = apps.get(i);
             //该应用的包名
             String pkg = info.activityInfo.packageName;
             //应用的主activity类
             String cls = info.activityInfo.name;
             ComponentName componet = new ComponentName(pkg, cls);

             Intent intent = new Intent();
             intent.setComponent(componet);
             startActivity(intent);
         }
     };

 private OnItemClickListener clickListener = new OnItemClickListener() {
         @Override
         public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
             ResolveInfo info = apps.get(i);
             //该应用的包名
             String pkg = info.activityInfo.packageName;
             //应用的主activity类
             String cls = info.activityInfo.name;
             ComponentName componet = new ComponentName(pkg, cls);


             Intent intent = new Intent();
             intent.setComponent(componet);
             startActivity(intent);
         }
     };

代码中的中文注释可能会引起Gradle报错

解决办法：http://blog.csdn.net/sljjyy/article/details/11976099

现在整个类代码如下：

 package com.sljjyy.sao.launcher;

 import android.content.ComponentName;
 import android.content.Intent;
 import android.content.pm.ResolveInfo;
 import android.os.Bundle;
 import android.app.Activity;
 import android.view.Menu;
 import android.view.View;
 import android.view.ViewGroup;
 import android.widget.AdapterView;
 import android.widget.BaseAdapter;
 import android.widget.GridView;
 import android.widget.ImageView;
 import android.widget.AdapterView.OnItemClickListener;

 import java.util.List;

 public class MainActivity extends Activity {
     GridView appsGrid;
     private List<ResolveInfo> apps;

     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
         loadApps();
         appsGrid = (GridView) findViewById(R.id.apps_list);
         appsGrid.setAdapter(new AppsAdapter());

         appsGrid.setOnItemClickListener(clickListener);
     }


     @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;
     }

     private OnItemClickListener clickListener = new OnItemClickListener() {
         @Override
         public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
             ResolveInfo info = apps.get(i);
             //该应用的包名
             String pkg = info.activityInfo.packageName;
             //应用的主activity类
             String cls = info.activityInfo.name;
             ComponentName componet = new ComponentName(pkg, cls);

             Intent intent = new Intent();
             intent.setComponent(componet);
             startActivity(intent);
         }
     };


     private void loadApps() {
         Intent mainIntent = new Intent(Intent.ACTION_MAIN, null);
         mainIntent.addCategory(Intent.CATEGORY_LAUNCHER);
         new ImageView(MainActivity.this);

         apps = getPackageManager().queryIntentActivities(mainIntent, 0);
     }


     public class AppsAdapter extends BaseAdapter {

         public AppsAdapter(){
         }

         @Override
         public int getCount() {
             return apps.size();
         }

         @Override
         public Object getItem(int i) {
             return apps.get(i);
         }

         @Override
         public long getItemId(int i) {
             return i;
         }


         @Override
         public View getView(int i, View view, ViewGroup viewGroup) {
             ImageView iv;

             if(view == null){
                 iv = new ImageView(MainActivity.this);
                 iv.setScaleType(ImageView.ScaleType.FIT_CENTER);
                 iv.setLayoutParams(new GridView.LayoutParams(50, 50));
             } else {
                 iv = (ImageView) view;
             }
             ResolveInfo info = apps.get(i);
             iv.setImageDrawable(info.activityInfo.loadIcon(getPackageManager()));
             return iv;
         }
     }
 }