android 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();
        }
    }
文章转载自互联网，感谢原作者的无私分享。