android实现程序的后台运行

</pre><pre name="code" class="java">	/**
* 改写返回键事件监听，使得back键功能类似home键，让Acitivty退至后台时不被系统销毁
*/
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
PackageManager pm = getPackageManager();
ResolveInfo homeInfo = pm.resolveActivity(
new Intent(Intent.ACTION_MAIN)
.addCategory(Intent.CATEGORY_HOME), 0);
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);
}

private void startActivitySafely(Intent intent) {
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
try {
startActivity(intent);
} catch (ActivityNotFoundException e) {
Toast.makeText(this, "null", Toast.LENGTH_SHORT).show();
} catch (SecurityException e) {
Toast.makeText(this, "null", Toast.LENGTH_SHORT).show();
}
}