@Override protected void onDestroy() { super.onDestroy(); unregisterReceiver(receiver); }
时间: 2023-07-15 17:11:10 浏览: 47
这段代码是在 Android 开发中的 Activity 类中的 onDestroy() 方法中的。它的作用是在 Activity 销毁时,取消注册之前注册的广播接收器(receiver),以免造成内存泄漏。
广播接收器是一个能够接收并响应特定广播消息的组件。在 Android 中,广播是一种系统级别的通信机制,可以跨应用程序发送和接收消息。当应用程序需要接收系统广播或者自定义广播时,就需要注册一个广播接收器。当广播消息到达时,系统会自动调用广播接收器中的 onReceive() 方法进行处理。
在 Activity 中注册广播接收器后,如果不及时取消注册,就有可能导致内存泄漏。因此,在 Activity 销毁时,需要调用 unregisterReceiver() 方法取消注册。
相关问题
public abstract class BaseFragment extends Fragment { static final String TAG = "tag"; public final String ACTION = "NIGHT_SWITCH"; protected BroadcastReceiver receiver; protected IntentFilter filter; @Override protected void onCreate(Bundle savedInstanceState){ super.onCreate(savedInstanceState); setNightMode(); filter = new IntentFilter(); filter.addAction(ACTION); receiver = new BroadcastReceiver() { @Override public void onReceive(Context context, Intent intent) { Log.d(TAG, "onReceive: needRefresh"); needRefresh(); } }; registerReceiver(receiver, filter); } public boolean isNightMode(){ SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(getBaseContext()); return sharedPreferences.getBoolean("nightMode", false); } public void setNightMode(){ if(isNightMode()) { SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(getBaseContext()); Log.d(TAG, "setNightMode: " + sharedPreferences.getBoolean("nightMode", false)); this.setTheme(R.style.NightTheme); } else setTheme(R.style.DayTheme); } @Override protected void onDestroy() { super.onDestroy(); unregisterReceiver(receiver); } protected abstract void needRefresh(); }这段代码有问题,怎么改
这段代码中的问题在于 `setTheme()` 方法不能在 Fragment 中使用,而应该在 Activity 中使用。因此,我们需要将设置主题的代码移到 Activity 中。以下是修改后的代码:
```
public abstract class BaseFragment extends Fragment {
static final String TAG = "tag";
public final String ACTION = "NIGHT_SWITCH";
protected BroadcastReceiver receiver;
protected IntentFilter filter;
@Override
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
filter = new IntentFilter();
filter.addAction(ACTION);
receiver = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
Log.d(TAG, "onReceive: needRefresh");
needRefresh();
}
};
requireActivity().registerReceiver(receiver, filter);
}
public boolean isNightMode(){
SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(requireContext());
return sharedPreferences.getBoolean("nightMode", false);
}
@Override
public void onDestroy() {
super.onDestroy();
requireActivity().unregisterReceiver(receiver);
}
protected abstract void needRefresh();
}
```
请注意,我们将 `registerReceiver()` 和 `unregisterReceiver()` 方法中的 `getContext()` 改为了 `requireContext()`,这是因为在 Fragment 中使用 `getContext()` 可能会返回 null,而 `requireContext()` 可以确保返回非 null 的 Context。
public abstract class BaseFragment extends Fragment { static final String TAG = "tag"; public final String ACTION = "NIGHT_SWITCH"; protected BroadcastReceiver receiver; protected IntentFilter filter; @Override public void onCreate(Bundle savedInstanceState){ super.onCreate(savedInstanceState); filter = new IntentFilter(); filter.addAction(ACTION); receiver = new BroadcastReceiver() { @Override public void onReceive(Context context, Intent intent) { Log.d(TAG, "onReceive: needRefresh"); needRefresh(); } }; requireActivity().registerReceiver(receiver, filter); } public boolean isNightMode(){ SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(requireContext()); return sharedPreferences.getBoolean("nightMode", false); } @Override public void onDestroy() { super.onDestroy(); requireActivity().unregisterReceiver(receiver); } protected abstract void needRefresh(); }怎么早mainactivity中引用isNightMode();
可以在MainActivity中创建一个BaseFragment的实例,然后通过该实例调用isNightMode()方法。例如:
```
public class MainActivity extends AppCompatActivity {
private BaseFragment mBaseFragment;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// 创建BaseFragment实例
mBaseFragment = new YourFragment();
// 调用isNightMode()方法
boolean isNightMode = mBaseFragment.isNightMode();
}
}
```
请注意,您需要将"YourFragment"替换为您自己的Fragment类名,并在该类中实现needRefresh()方法。