Android 实现Activity后台运行

		PackageManager pm = getPackageManager();
                                ResolveInfo homeInfo = pm.resolveActivity(new Intent(Intent.ACTION_MAIN)
		.addCategory(Intent.CATEGORY_HOME), 0);

	public boolean onKeyDown(int keyCode, KeyEvent event) {
		if (keyCode == KeyEvent.KEYCODE_BACK) {
			ActivityInfo ai = homeInfo.activityInfo;
			Intent startIntent = new Intent(Intent.ACTION_MAIN);
			startIntent.addCategory(Intent.CATEGORY_LAUNCHER);
			startIntent.setComponent(new ComponentName(ai.packageName,
					ai.name));
			startActivitySafely(startIntent);
			return true;
		} else
			return super.onKeyDown(keyCode, event);
	}

	void startActivitySafely(Intent intent) {
		intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
		try {
			startActivity(intent);
		} catch (ActivityNotFoundException e) {
			Toast.makeText(this, R.string.unabletoopensoftware,
					Toast.LENGTH_SHORT).show();
		} catch (SecurityException e) {
			Toast.makeText(this, R.string.unabletoopensoftware,
					Toast.LENGTH_SHORT).show();
			Log
					.e(
							TAG,
							"Launcher does not have the permission to launch "
									+ intent
									+ ". Make sure to create a MAIN intent-filter for the corresponding activity "
									+ "or use the exported attribute for this activity.",
							e);
		}
	}