java – 第二个FragmentTransaction.replace()调用的Android Fragment转换错误
作者：互联网
我在我的mainActivity.java的classic_menu.xml中的fragment_container中保存了3种类型的片段.我从片段A开始,按下按钮,通过我使用FragmentTransaction.replace(R.id.fragment_container,B)的方法转到片段B.当我希望使用相同的方法从B转到片段C时,问题出现了.我使用你在下面看到的内容得到了一个投射错误.编辑我通过使用findFragmentByTag()而不是findFragmentById()得到一个空指针.
以下是有问题的片段：
片段A：
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import com.example.R;
public class MainMenuFragment extends Fragment{
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle onSavedInstanceState){
View view = inflater.inflate(R.layout.main_menu_fragment, container, false);
return view;
}
}
片段B：
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import com.example.R;
public class ClassicMenuFragment extends Fragment{
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle onSavedInstanceState){
View view = inflater.inflate(R.layout.classic_menu_fragment, container, false);
return view;
}
}
片段C：
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import com.example.MainActivity;
import com.example.R;
import com.example.widgets.TextViewPlus;
public class OnePlayerFragment extends Fragment{
private static TextViewPlus topScore;
private static TextViewPlus bottomScore;
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle onSavedInstanceState){
View view = inflater.inflate(R.layout.one_player_fragment, container, false);
topScore = (TextViewPlus) view.findViewById(R.id.topPlayerScore1P);
bottomScore = (TextViewPlus) view.findViewById(R.id.bottomPlayerScore1P);
return view;
}
/**
* Changes the text of certain textViewPlus objects based on the given score
* @param view int value that determines which view to update
* @param score value to set the text to
*/
public void setScore(int view, int score){
if(view == MainActivity.TOP_PLAYER_1P) topScore.setText("" + score);
else if(view == MainActivity.BOTTOM_PLAYER) bottomScore.setText("" + score);
}
}
正在使用的按钮：
// in main_menu_fragment.xml
<com.example.widgets.ButtonPlus
android:id="@+id/classicB"
style="@style/button"
android:onClick="StartClassicMenu"/>
// in classic_menu_fragment.xml
<com.example.widgets.ButtonPlus
android:id="@+id/onePlayerB"
style="@style/button"
android:onClick="StartGame"/>
MainActivity.java：
// cut a lot of stuff for brevity
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentTransaction;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.TextView;
import com.example.fragments.ClassicMenuFragment;
import com.example.fragments.MainMenuFragment;
import com.example.fragments.OnePlayerFragment;
public class MainActivity extends FragmentActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.classic_menu);
// cut more stuff
theView = (GameView)findViewById(R.id.theView); // get reference to the GameView
// begin the game in Animation mode and pass this MainActivity to the GameView so it can be passed along
theView.initiateGameThread(GameState.ANIMATION_MODE, this);
theThread = theView.getThread(); // get reference to the GameThread
theGame = theThread.getGameState(); // get reference to the GameState
if (findViewById(R.id.fragment_container) != null) {
if (savedInstanceState != null) return;
MainMenuFragment mMenu = new MainMenuFragment();
// Add the fragment to the 'fragment_container' FrameLayout
getSupportFragmentManager().beginTransaction().add(R.id.fragment_container, mMenu).commit();
}
}
public void StartClassicMenu(View v){
changeToFragment(new ClassicMenuFragment(), "ClassicMenu");
inFragment = true;
}
public void StartGame(View v){
switch (v.getId()){
case R.id.onePlayerB:
theGame.setMode(GameState.ONE_PLAYER_MODE);
changeToFragment(new OnePlayerFragment(), "OnePlayer");
Log.d("MainActivity", "StartGame() for 1P mode called");
break;
// other cases here but cut out
theGame.reset();
}
// called from gamestate when views need to be updated
public void setViewScore(int view, int score){
if(theGame.getMode() == GameState.ONE_PLAYER_MODE){
Log.d("MainActivity", "setViewScore() for 1P mode called");
OnePlayerFragment f = (OnePlayerFragment) getSupportFragmentManager().findFragmentById(R.id.fragment_container);
if(f == null) Log.d("OnePlayerFragment", "null!!!");
f.setScore(view, score);
}
// other cases cut out
}
/**
* Handles creating and managing a uniform FragmentTransaction for the entire app
* @param newFragment the new Fragment that will fade in, replacing whichever fragment was in use
*/
public void changeToFragment(Fragment newFragment, String tag){
Log.d("MainActivity", "changeToFragment() Called with tag \"" + tag + "\"");
// Create the standard fade in/out transaction
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
transaction.setCustomAnimations(android.R.anim.fade_in, android.R.anim.fade_out);
// Replace the old fragment in the Relative Layout view with the new one
transaction.replace(R.id.fragment_container, newFragment, tag);
transaction.commit(); // Commit the transaction
}
MainActivity的xml布局文件：
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@color/back_grey">
<com.example.GameView
android:id="@+id/theView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_gravity="center" />
<RelativeLayout
android:id="@+id/rLayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:scaleType="centerCrop">
<FrameLayout
android:id="@+id/fragment_container"
android:layout_width="match_parent"
android:layout_height="match_parent">
</FrameLayout>
</RelativeLayout>
而现在最好的部分：
07-18 16:30:01.999: D/OpenGLRenderer(12335): Enabling debug mode 0
07-18 16:30:02.259: D/GameView(12335): surfaceCreated() Called
07-18 16:30:02.649: I/Timeline(12335): Timeline: Activity_idle id: android.os.BinderProxy@1f1e5333 time:475861093
07-18 16:30:13.179: D/ViewRootImpl(12335): ViewPostImeInputStage ACTION_DOWN
07-18 16:30:13.389: D/MainActivity(12335): changeToFragment() Called with tag "ClassicMenu"
07-18 16:30:14.099: D/ViewRootImpl(12335): ViewPostImeInputStage ACTION_DOWN
07-18 16:30:14.169: D/MainActivity(12335): changeToFragment() Called with tag "OnePlayer"
07-18 16:30:14.169: D/MainActivity(12335): StartGame() for 1P mode called
07-18 16:30:14.179: D/MainActivity(12335): setViewScore() for 1P mode called
07-18 16:30:14.219: D/AndroidRuntime(12335): Shutting down VM
07-18 16:30:14.249: E/AndroidRuntime(12335): FATAL EXCEPTION: main
07-18 16:30:14.249: E/AndroidRuntime(12335): Process: com.brownapps.battlepong, PID: 12335
07-18 16:30:14.249: E/AndroidRuntime(12335): java.lang.IllegalStateException: Could not execute method of the activity
07-18 16:30:14.249: E/AndroidRuntime(12335): at android.view.View$1.onClick(View.java:4222)
07-18 16:30:14.249: E/AndroidRuntime(12335): at android.view.View.performClick(View.java:5156)
07-18 16:30:14.249: E/AndroidRuntime(12335): at android.view.View$PerformClick.run(View.java:20755)
07-18 16:30:14.249: E/AndroidRuntime(12335): at android.os.Handler.handleCallback(Handler.java:739)
07-18 16:30:14.249: E/AndroidRuntime(12335): at android.os.Handler.dispatchMessage(Handler.java:95)
07-18 16:30:14.249: E/AndroidRuntime(12335): at android.os.Looper.loop(Looper.java:145)
07-18 16:30:14.249: E/AndroidRuntime(12335): at android.app.ActivityThread.main(ActivityThread.java:5835)
07-18 16:30:14.249: E/AndroidRuntime(12335): at java.lang.reflect.Method.invoke(Native Method)
07-18 16:30:14.249: E/AndroidRuntime(12335): at java.lang.reflect.Method.invoke(Method.java:372)
07-18 16:30:14.249: E/AndroidRuntime(12335): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
07-18 16:30:14.249: E/AndroidRuntime(12335): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
07-18 16:30:14.249: E/AndroidRuntime(12335): Caused by: java.lang.reflect.InvocationTargetException
07-18 16:30:14.249: E/AndroidRuntime(12335): at java.lang.reflect.Method.invoke(Native Method)
07-18 16:30:14.249: E/AndroidRuntime(12335): at java.lang.reflect.Method.invoke(Method.java:372)
07-18 16:30:14.249: E/AndroidRuntime(12335): at android.view.View$1.onClick(View.java:4217)
07-18 16:30:14.249: E/AndroidRuntime(12335): ... 10 more
07-18 16:30:14.249: E/AndroidRuntime(12335): Caused by: java.lang.ClassCastException: com.example.fragments.ClassicMenuFragment cannot be cast to com.example.fragments.OnePlayerFragment
07-18 16:30:14.249: E/AndroidRuntime(12335): at com.example.MainActivity.setViewScore(MainActivity.java:325)
07-18 16:30:14.249: E/AndroidRuntime(12335): at com.example.GameState$5.run(GameState.java:650)
07-18 16:30:14.249: E/AndroidRuntime(12335): at android.app.Activity.runOnUiThread(Activity.java:5517)
07-18 16:30:14.249: E/AndroidRuntime(12335): at com.example.GameState.reset(GameState.java:647)
07-18 16:30:14.249: E/AndroidRuntime(12335): at com.example.MainActivity.StartGame(MainActivity.java:146)
07-18 16:30:14.249: E/AndroidRuntime(12335): ... 13 more
您可能需要的唯一其他信息是,在游戏的reset()方法中,它通过View.initiateGameThread(GameState.ANIMATION_MODE,this)调用传递给它的MainActivity对象上的setViewScore();通过使用runOnUiThread().
所以,我的问题是,为什么我第一次调用changeToFragment()会将MainMenuFragment更改为ClassicMenuFragment,但是当它应该将ClassicMenuFragment更改为OnePlayerFragment时第二次搞砸了？
感谢您花时间考虑我的这个问题.
解决方法:
ClassCastException是正确的 – 您无法将ClassicMenuFragment强制转换为OnePlayerFragment.在继承方面,你不能将一个兄弟转换为另一个兄弟(这两个类都是兄弟姐妹,有一个共同的父片段).一个类比是Orange和Apple都是一类Fruit的孩子,但是你不能把橘子扔给Apple(这没有意义！)
相反,将您的强制转换移除到OnePlayerFragment并使用instanceof关键字,只有在您确定片段是哪个子实例时才进行强制转换：
Fragment f = getSupportFragmentManager().findFragmentById(R.id.fragment_container);
if (f == null) Log.d("Fragment", "null!!!");
if (f instanceof OnePlayerFragment) {
((OnePlayerFragment) f).setScore(view, score);
}
标签：java,android,android-fragments,classcastexception,fragmenttransaction 来源： https://codeday.me/bug/20190628/1316028.html