首先DialogFragment是跟随Fragment一起被Google推出的,DialogFragment是基于Fragment的,生命周期和Fragment是一样的。
在Android中,实现对话框的方式多种:
- Dialog/Alter
- DialogFragment
- Activity的Style设置成Dialog
通常,我们在开发中实现通过继承Dialog来实现对话框的效果,但是,基于Dialog的对话框生命周期是不会随着Activity的,我们可以写一段简单的代码来看看:
public class MyDialogActivity extends AppCompatActivity { private static final String TAG = "MyDialogActivity"; @Override protected void onCreate(@Nullable Bundle savedInstanceState) { super.onCreate(savedInstanceState); Log.e(TAG,"onCreate"); setContentView(R.layout.activity_dialog); Button button = findViewById(R.id.button4); button.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { MyDialog myDialog = new MyDialog(MyDialogActivity.this); myDialog.show(); } }); //延时2秒主动关闭Activity Handler handler = new Handler(); handler.postDelayed(new Runnable() { @Override public void run() { finish(); } },2000); } @Override protected void onResume() { super.onResume(); Log.e(TAG,"onResume"); } @Override protected void onStart() { super.onStart(); Log.e(TAG,"onStart"); } @Override protected void onRestart() { super.onRestart(); Log.e(TAG,"onRestart"); } @Override protected void onPause() { super.onPause(); Log.e(TAG,"onPause"); } @Override protected void onDestroy() { super.onDestroy(); Log.e(TAG,"onDestroy"); } @Override protected void onStop() { super.onStop(); Log.e(TAG,"onStop"); } static class MyDialog extends Dialog { private String TAG = "Dialog"; public MyDialog(@NonNull Context context) { super(context); setContentView(R.layout.dialog_demo); } @Override protected void onStop() { super.onStop(); Log.e(TAG,"onStop"); } @Override protected void onStart() { super.onStart(); Log.e(TAG,"onStart"); } @Override public void cancel() { super.cancel(); Log.e(TAG,"cancel"); } @Override public void dismiss() { super.dismiss(); Log.e(TAG,"dismiss"); } @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); Log.e(TAG,"onCreate"); } } }
运行起来后,打开一个Dialog,然后延时两秒关闭Dialog,发现Log中竟然报错了:
大致的意思,Dialog没被关闭,造成了内存泄漏
解决办法也很简单,在Activity中的onDestory方法中主动关闭:
@Override protected void onDestroy() { super.onDestroy(); if (myDialog != null){ myDialog.cancel(); } Log.e(TAG,"onDestroy"); }
如果每次都要这样做,感觉比较繁琐,为什么不能让系统自己来回收呢?这里就可以使用DialogFragment:
public class MyDialogFragment extends DialogFragment { private static final String TAG = "MyDialogFragment"; @Override public void onCreate(@Nullable Bundle savedInstanceState) { super.onCreate(savedInstanceState); Log.d(TAG,"onCreate"); } @Nullable @Override public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) { Log.d(TAG,"onCreateView"); return super.onCreateView(inflater, container, savedInstanceState); } @Override public void onDetach() { super.onDetach(); Log.d(TAG,"onDetach"); } @Override public void onDestroy() { super.onDestroy(); Log.d(TAG,"onDestroy"); } }
从日志来看,当Activity生命周期发生变化的时候,DialogFragment的生命周期也在发生变化,这和Fragment是一样的,因此可以保证当对话框的生命周期和Activity的生命周期保持一致,避免内存泄漏
顺便提一下,在通过点击弹出对话框的时候,不要直接new一个对话框,如果可以复用,就尽量复用,减少对象的创建