（一） 通过包名、类名

开发有时需要在一个应用中启动另一个应用，比如Launcher加载所有的已安装的程序的列表，当点击图标时可以启动另一个应用。一般我们知道了另一个应用的包名和MainActivity的名字之后便可以直接通过如下代码来启动：

Intent intent = new Intent(Intent.ACTION_MAIN);
intent.addCategory(Intent.CATEGORY_LAUNCHER);
ComponentName cn = new ComponentName(packageName, className);
intent.setComponent(cn);
startActivity(intent);

但是更多的时候，我们一般都不知道目标应用程序的启动Activity的类名，而只知道包名，接下来就需要这么做了，我封装成了一个方法，如下所示：

               private void doStartApplicationWithPackageName(String packagename) {                        // 通过包名获取此APP详细信息，包括Activities、services、versioncode、name等等              PackageInfo packageinfo = null;              try {                  packageinfo = getPackageManager().getPackageInfo(packagename, 0);              } catch (NameNotFoundException e) {                  e.printStackTrace();              }              if (packageinfo == null) {                  return;              }                        // 创建一个类别为CATEGORY_LAUNCHER的该包名的Intent              Intent resolveIntent = new Intent(Intent.ACTION_MAIN, null);              resolveIntent.addCategory(Intent.CATEGORY_LAUNCHER);              resolveIntent.setPackage(packageinfo.packageName);                        // 通过getPackageManager()的queryIntentActivities方法遍历              List<ResolveInfo> resolveinfoList = getPackageManager()                      .queryIntentActivities(resolveIntent, 0);                        ResolveInfo resolveinfo = resolveinfoList.iterator().next();              if (resolveinfo != null) {                  // packagename = 参数packname                  String packageName = resolveinfo.activityInfo.packageName;                  // 这个就是我们要找的该APP的LAUNCHER的Activity[组织形式：packagename.mainActivityname]                  String className = resolveinfo.activityInfo.name;                  // LAUNCHER Intent                  Intent intent = new Intent(Intent.ACTION_MAIN);                  intent.addCategory(Intent.CATEGORY_LAUNCHER);                            // 设置ComponentName参数1:packagename参数2:MainActivity路径                  ComponentName cn = new ComponentName(packageName, className);                            intent.setComponent(cn);                  startActivity(intent);              }          }
private void doStartApplicationWithPackageName(String packagename) {

    // 通过包名获取此APP详细信息，包括Activities、services、versioncode、name等等
    PackageInfo packageinfo = null;
    try {
        packageinfo = getPackageManager().getPackageInfo(packagename, 0);
    } catch (NameNotFoundException e) {
        e.printStackTrace();
    }
    if (packageinfo == null) {
        return;
    }

    // 创建一个类别为CATEGORY_LAUNCHER的该包名的Intent
    Intent resolveIntent = new Intent(Intent.ACTION_MAIN, null);
    resolveIntent.addCategory(Intent.CATEGORY_LAUNCHER);
    resolveIntent.setPackage(packageinfo.packageName);

    // 通过getPackageManager()的queryIntentActivities方法遍历
    List<ResolveInfo> resolveinfoList = getPackageManager()
            .queryIntentActivities(resolveIntent, 0);

    ResolveInfo resolveinfo = resolveinfoList.iterator().next();
    if (resolveinfo != null) {
        // packagename = 参数packname
        String packageName = resolveinfo.activityInfo.packageName;
        // 这个就是我们要找的该APP的LAUNCHER的Activity[组织形式：packagename.mainActivityname]
        String className = resolveinfo.activityInfo.name;
        // LAUNCHER Intent
        Intent intent = new Intent(Intent.ACTION_MAIN);
        intent.addCategory(Intent.CATEGORY_LAUNCHER);

        // 设置ComponentName参数1:packagename参数2:MainActivity路径
        ComponentName cn = new ComponentName(packageName, className);

        intent.setComponent(cn);
        startActivity(intent);
    }
}