android实现程序的后台运行

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，代码如下：

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();

}

}

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