Android系统存在多个Launcher时，设置开机进入默认的Launcher

问题提出：

      当系统存在多个Launcher时，开机完成并解锁后，系统会弹出一个选择框让用户选择
进入哪一个Launcher，如果不想选择，而是想直接进入某一个默认的Launcher，并且
用户在设置->应用程序->管理应用程序->所有应用程序列表，找到之前设置的那个默
认的Launcher，并且取消了默认值，可以重新弹出launcher选框。

解决方法：

      下面以设置Google Launcher2作为默认启动的Launcher为例，
其package name 为 com.android.launcher
launcher activity name 为 com.android.launcher2.Launcher

需要以下两个修改点

1）修改Provision应用

编辑packages/apps/Provision/src/com/android/DefaultActivity.java文件

/* * Copyright (C) 2008 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * *      http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */package com.android.provision;import android.app.Activity;import android.content.ComponentName;import android.content.Intent;import android.content.IntentFilter;import android.content.pm.PackageManager;import android.content.pm.ResolveInfo;import android.os.Bundle;import android.provider.Settings;import android.util.Log;import java.util.List;/** * Application that sets the provisioned bit, like SetupWizard does. */public class DefaultActivity extends Activity {    private static final String TAG = "DefaultActivity";    @Override    protected void onCreate(Bundle icicle) {        super.onCreate(icicle);        //新增这个函数的调用        setupDefaultLauncher();        // Add a persistent setting to allow other apps to know the device has been provisioned.        Settings.Global.putInt(getContentResolver(), Settings.Global.DEVICE_PROVISIONED, 1);        // remove this activity from the package manager.        PackageManager pm = getPackageManager();        ComponentName name = new ComponentName(this, DefaultActivity.class);        pm.setComponentEnabledSetting(name, PackageManager.COMPONENT_ENABLED_STATE_DISABLED,                PackageManager.DONT_KILL_APP);        // terminate the activity.        finish();    }    private void setupDefaultLauncher() {        // remove this activity from the package manager.        PackageManager pm = getPackageManager();        String examplePackageName = "com.bluegod.launcher"; //请修改为需要设置的 package name        String exampleActivityName = "com.android.launcher2.Launcher"; //请修改为需要设置的 launcher activity name        ComponentName defaultLauncher = null;        Intent intent = new Intent(Intent.ACTION_MAIN);        intent.addCategory(Intent.CATEGORY_HOME);        List<ResolveInfo> resolveInfoList =                pm.queryIntentActivities(intent, 0);        if (resolveInfoList != null) {            int size = resolveInfoList.size();            for (int j = 0; j < size; ) {                final ResolveInfo r = resolveInfoList.get(j);                if (!r.activityInfo.packageName.equals(examplePackageName)) {                    resolveInfoList.remove(j);                    size -= 1;                } else {                    j++;                }            }            ComponentName[] set = new ComponentName[size];            defaultLauncher = new ComponentName(examplePackageName, exampleActivityName);            int defaultMatch = 0;            for (int i = 0; i < size; i++) {                final ResolveInfo resolveInfo =                        resolveInfoList.get(i);                Log.d(TAG, resolveInfo.toString());                set[i] = new                        ComponentName(resolveInfo.activityInfo.packageName, resolveInfo.activityInfo.name);                if (defaultLauncher.getClassName().equals(resolveInfo.activityInfo.name)) {                    defaultMatch = resolveInfo.match;                }            }            Log.d(TAG, "defaultMatch =" + Integer.toHexString(defaultMatch));            IntentFilter filter = new IntentFilter();            filter.addAction(Intent.ACTION_MAIN);            filter.addCategory(Intent.CATEGORY_HOME);            filter.addCategory(Intent.CATEGORY_DEFAULT);            pm.clearPackagePreferredActivities(defaultLauncher.getPackageName());            pm.addPreferredActivity(filter, defaultMatch, set, defaultLauncher);        }    }}

在setComponentEnabledSetting函数调用之前，新增setupDefaultLauncher()函数的调用。

然后修改packages/apps/Provision/AndroidManifest.xml文件，增加以下语句：
<uses-permission android:name=”android.permission.SET_PREFERRED_APPLICATIONS” />

2）修改框架文件修改 PackageManagerService.java

framework/base/services/java/com/android/server/pm/PackageManagerService.java该文件中找到 findPreferredActivity 方法
，将此方法的比较靠后的一段代码if (!pa.mPref.sameSet(query, priority)) { 添加如下语句

// Okay we found a previously set preferred app.            // If the result set is different from when this            // was created, we need to clear it and re-ask the            // user their preference.            /*if (!pa.mPref.sameSet(query, priority)) {                Slog.i(TAG, "Result set changed, dropping preferred activity for "                        + intent + " type " + resolvedType);                pir.removeFilter(pa);                return null;            }*/            if (!pa.mPref.sameSet(query, priority)) {                if (!(intent.getAction() != null                        && intent.getAction().equals(intent.ACTION_MAIN)                        && intent.getCategories() != null                        && intent.getCategories().contains(intent.CATEGORY_HOME))) //添加                {  //添加这行                    Slog.i(TAG, "Result set changed, dropping preferred activity: "                            + intent + " type " + resolvedType);                    pir.removeFilter(pa);                    return null;                }  //添加这行                Slog.i(TAG, "Result set not change, not drop preferred activity special intent: " + intent);//添加这行            }

替换上面/* */注释部分的代码，说白了主要增加一个if语句的判断

if (!(intent.getAction() != null                        && intent.getAction().equals(intent.ACTION_MAIN)                        && intent.getCategories() != null                        && intent.getCategories().contains(intent.CATEGORY_HOME)))

如果非Launcher，则执行removeFilter()。

OK，经过以上两个修改，就可以做到开机后设置Google Launcher2作为默认启动的Launcher