Java 在backstack中添加新片段时调用两次onBackStackChanged()
所以,我注意到了一个有趣的问题。当我以编程方式添加新片段时,从OnBackbackChangedListener调用OnBackbackChanged方法两次,但只能调用一次。以下是我的活动代码:Java 在backstack中添加新片段时调用两次onBackStackChanged(),java,android,android-fragments,android-view,fragmentmanager,Java,Android,Android Fragments,Android View,Fragmentmanager,所以,我注意到了一个有趣的问题。当我以编程方式添加新片段时,从OnBackbackChangedListener调用OnBackbackChanged方法两次,但只能调用一次。以下是我的活动代码: import android.os.Bundle; import android.support.v4.app.Fragment; import android.support.v4.app.FragmentManager; import android.support.v7.app.AppCompa
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.Button;
public class MainActivity extends AppCompatActivity implements FragmentManager.OnBackStackChangedListener{
private FragmentManager fragmentManager;
private Button button1;
private Button button2;
private Button button3;
private Fragment defaultFragment;
private Fragment previousFragment;
private Fragment currentFragment;
private String currentFragmentTag;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button1 = (Button) findViewById(R.id.button);
button2 = (Button) findViewById(R.id.button2);
button3 = (Button) findViewById(R.id.button3);
button1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
showFragment(new FragmentOne(), FragmentOne.TAG);
}
});
button2.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
showFragment(new FragmentTwo(), FragmentTwo.TAG);
}
});
button3.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
showFragment(new FragmentThree(), FragmentThree.TAG);
}
});
setupFragmentManager();
}
private void setupFragmentManager() {
fragmentManager = getSupportFragmentManager();
fragmentManager.addOnBackStackChangedListener(this);
FragmentOne fragmentOne = new FragmentOne();
defaultFragment = fragmentOne; // fragment for default
currentFragmentTag = FragmentOne.TAG;
currentFragment = fragmentOne;
fragmentManager.beginTransaction()
.add(R.id.fragments_container, currentFragment, currentFragmentTag)
.addToBackStack(currentFragmentTag)
.commit();
}
public void showFragment(Fragment fragment, String fragmentTag) {
previousFragment = currentFragment;
currentFragment = fragment;
fragmentManager.beginTransaction()
.hide(previousFragment)
.add(R.id.fragments_container, fragment, fragmentTag)
.addToBackStack(fragmentTag)
.commit();
}
@Override
public void onBackStackChanged() {
Log.d("MY_TAG" , "onBackStackChangedListener - " + fragmentManager.getBackStackEntryCount() );
if (fragmentManager.getBackStackEntryCount() > 0) {
String fragmentTag = fragmentManager.getBackStackEntryAt(fragmentManager.getBackStackEntryCount() - 1).getName();
currentFragment = fragmentManager.findFragmentByTag(fragmentTag);
} else {
currentFragment = defaultFragment;
}
// some code...
}
@Override
public void onBackPressed() {
if (fragmentManager.getBackStackEntryCount() == 1) {
finish();
} else {
super.onBackPressed();
}
}
}
和片段类:
public class FragmentOne extends Fragment {
public static final String TAG = FragmentOne.class.getSimpleName();
private Context context;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
context = getActivity();
View topLevelView = LayoutInflater.from(context).inflate(R.layout.fragment_layout, container, false);
TextView textView = (TextView) topLevelView.findViewById(R.id.fragment_Text);
textView.setText("This is FRAGMENT ONE");
return topLevelView;
}
}
碎片2和碎片3与碎片1相同
当我启动我的应用程序时,在日志中我看到:
onBackStackChangedListener - 1
onBackStackChangedListener - 1
按下按钮(显示下一个片段)后,我看到:
还有一个:
onBackStackChangedListener - 3
onBackStackChangedListener - 3
改变
.add(R.id.fragments_container, currentFragment, currentFragmentTag)
到
这并不能解决问题
但这很奇怪。为什么我的OnBackbackChangedListener在添加片段后多次调用own方法?简直不敢相信这会发生。创建了一个类似的项目并深入到调试器中。原来这是新支持库中的一个bug。有一个 切换回
25.0.0
将按预期工作
compile 'com.android.support:appcompat-v7:25.0.0'
compile 'com.android.support:support-v4:25.0.0'
虽然没有在中提到,但已经提到,该问题在
25.4.0
中得到了解决,这很好只是一个更新。谷歌最终发布了25.4.0版,解决了这个问题
只是,现在支持的内容是从Google的Maven存储库中获取的:
maven { url 'https://maven.google.com' }
因此,您可以开始使用所有内容的新版本,并从SDK管理器中卸载本地支持存储库。否,当我删除第行:.hide(previousFragment)-它无法解决问题。在添加第一个(默认)片段时没有隐藏方法。因此,这个问题并不取决于隐藏方法。实际上与您的问题无关,但您可以将View.OnClickListener接口直接实现到活动,并且对于每个按钮,
button.setOnClickListener(this)
,然后在活动中只需要一个onClick
方法,并使用switch语句查找单击的视图,并从单个实现运行逻辑,而不是在每次有需要单击行为的视图时定义它。
compile 'com.android.support:appcompat-v7:25.0.0'
compile 'com.android.support:support-v4:25.0.0'
maven { url 'https://maven.google.com' }