Android Launcher--简易Launcher开发

 第一步，把我们的应用程序作为home（即实现按下home键，启动自己的launcher.）

要把我们的应用程序作为home，只需要在AndroidManifest.xml中添加：
 <category android:name="android.intent.category.HOME" />
 <category android:name="android.intent.category.DEFAULT" />

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="org.bangchui.myhome"
      android:versionCode="1"
      android:versionName="1.0">

    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <activity android:name=".MyHome"
                  android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
                <category android:name="android.intent.category.HOME" />
                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>

    </application>
</manifest>

第二步，列出安装的应用程序

列出已经安装的应用程序是作为launcher比不可少的功能。下面我们就讲解怎样将应用程序列出来。程序运行后的样子如下：

1. 修改main.xml，在其中添加一个GridView用来显示应用程序列表。

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="fill_parent"
    android:layout_height="fill_parent">
     
    <GridView android:layout_width="match_parent"
        android:id="@+id/apps_list"
        android:numColumns="4"
        android:layout_height="wrap_content">
    </GridView>
 
</LinearLayout

2 . 通过PackageManager的api 查询已经安装的apk

private void loadApps() {
        Intent mainIntent = new Intent(Intent.ACTION_MAIN, null);
        mainIntent.addCategory(Intent.CATEGORY_LAUNCHER);
 
        mApps = getPackageManager().queryIntentActivities(mainIntent, 0);
    }

3. 实现用于显示Gridview的Adapter，使其显示获得的应用程序列表

public class AppsAdapter extends BaseAdapter {
        public AppsAdapter() {
        }
 
        public View getView(int position, View convertView, ViewGroup parent) {
            ImageView i;
 
 
            if (convertView == null) {
                i = new ImageView(MyHome.this);
                i.setScaleType(ImageView.ScaleType.FIT_CENTER);
                i.setLayoutParams(new GridView.LayoutParams(50, 50));
            } else {
                i = (ImageView) convertView;
            }
 
            ResolveInfo info = mApps.get(position);
            i.setImageDrawable(info.activityInfo.loadIcon(getPackageManager()));
 
            return i;
        }
 
        public final int getCount() {
            return mApps.size();
        }
 
        public final Object getItem(int position) {
            return mApps.get(position);
        }
 
        public final long getItemId(int position) {
            return position;
        }
    

4.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mGrid.setOnItemClickListener(listener); 设置一个监听器
mGrid.setOnItemClickListener(listener)中的listener是一个接口，其类型为：android.widget.AdapterView.OnItemClickListener

private OnItemClickListener listener = new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position,long id) {
//事件内容....
}
};

5.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：

 public void onItemClick(AdapterView<?> parent, View view, int position,long id) {
            ResolveInfo info = mApps.get(position);
             
            //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 i = new Intent();
            i.setComponent(componet);
            startActivity(i);
        }

最后整个Activity的代码如下：

package org.bangchui.myhome;

import java.util.List;

import android.app.Activity;
import android.content.ComponentName;
import android.content.Intent;
import android.content.pm.ResolveInfo;
import android.os.Bundle;
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;

public class MyHome extends Activity {
    private List<ResolveInfo> mApps;
    GridView mGrid;
    private OnItemClickListener listener = new OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position,long id) {
            ResolveInfo info = mApps.get(position);
            
            //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 i = new Intent();
            i.setComponent(componet);
            startActivity(i);
        }

    };

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        loadApps();
        setContentView(R.layout.main);
        mGrid = (GridView) findViewById(R.id.apps_list);
        mGrid.setAdapter(new AppsAdapter());

        mGrid.setOnItemClickListener(listener);
    }


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

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

    public class AppsAdapter extends BaseAdapter {
        public AppsAdapter() {
        }

        public View getView(int position, View convertView, ViewGroup parent) {
            ImageView i;

            if (convertView == null) {
                i = new ImageView(MyHome.this);
                i.setScaleType(ImageView.ScaleType.FIT_CENTER);
                i.setLayoutParams(new GridView.LayoutParams(50, 50));
            } else {
                i = (ImageView) convertView;
            }

            ResolveInfo info = mApps.get(position);
            i.setImageDrawable(info.activityInfo.loadIcon(getPackageManager()));

            return i;
        }

        public final int getCount() {
            return mApps.size();
        }

        public final Object getItem(int position) {
            return mApps.get(position);
        }

        public final long getItemId(int position) {
            return position;
        }
    }
}