有时，需要在应用程序中调用其他Android上已经安装完好的应用程序，
以下是一个调用相机(com.android.camera)的demo程序:
PackageInfo pi = null;
try {
//获得相机包名信息
pi = getPackageManager().getPackageInfo("com.android.camera", 0);
} catch (NameNotFoundException e) {
e.printStackTrace();
}
//获得当前应用程序的包管理器
PackageManager pm = MainActivity.this.getPackageManager();
Intent resolveIntent = new Intent(Intent.ACTION_MAIN, null);
resolveIntent.addCategory(Intent.CATEGORY_LAUNCHER);
resolveIntent.setPackage(pi.packageName);
List<ResolveInfo> apps = pm.queryIntentActivities(resolveIntent, 0);
ResolveInfo ri = apps.iterator().next();
if (ri != null ) {
String packageName = ri.activityInfo.packageName;
String className = ri.activityInfo.name;
Intent intent = new Intent(Intent.ACTION_MAIN);
intent.addCategory(Intent.CATEGORY_LAUNCHER);
ComponentName cn = new ComponentName(packageName, className);
intent.setComponent(cn);
startActivity(intent);
}
