Question

我知道这个问题曾被问到好几次，但我看到答案总是会因代码而改变。

所以，我有GameActivity从全局＆＃34; info＆＃34;中的数据库中检索信息。变量，即String []。

接下来，我需要将当前片段替换为与按下的按钮相关的另一个片段（请参阅方法＆＃34; trueAnswer＆＃34;＆＃34; falseAnswer＆＃34;），并设置该新片段的两个TextView使用＆＃34; info＆＃34;中检索到的信息;字符串数组。

问题在于我能够在创建活动时在onStart（）方法的第一个片段中第一次设置信息，但后来看起来就像＆＃34; info＆＃34;数组为空，因为＆＃34; if＆＃34;在方法＆＃34; trueAnswer＆＃34;和＆＃34; falseAnswer＆＃34;不起作用，当我尝试使用方法＆＃34; changeText（String，String）＆＃34;在新片段中设置TextView时，应用程序崩溃并返回NullPointerExeption。

我无法真正看到代码中的错误在哪里，所以我在这里发布我的方法和logCat，希望这对你也有所帮助。

GameActivity：

import java.io.IOException;

import android.content.SharedPreferences;
import android.database.SQLException;
import android.graphics.Color;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentTransaction;
import android.support.v7.app.ActionBarActivity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.FrameLayout;
import android.widget.TextView;
import android.widget.Toast;

public class GameActivity extends ActionBarActivity {

public long n = 0;
public String[] info = new String[3];

DataBase myDbHelper = new DataBase(this);

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_game);

    if (savedInstanceState == null) {
        getSupportFragmentManager().beginTransaction()
                .replace(R.id.container, new PlaceholderFragment()).commit();
    }
}

public void randomize(){

    n = Math.round((Math.random()*3)+1);

}

public String[] getDatabaseInfo(){

    myDbHelper.refresh();

    try {
        myDbHelper.createDataBase();
    } catch (IOException ioe) {
    throw new Error("NON HO CARICATO IL DATABASE TI PREGO SCUSAMI");
    }

    try {
        myDbHelper.openDataBase();
    }catch(SQLException sqle){
        throw sqle;
    }

    return info = myDbHelper.getQuestion(n);

}

@Override
public void onStart(){
    super.onStart();

    randomize();

    getDatabaseInfo();

    TextView d = (TextView)findViewById(R.id.question);
    d.setText(info[1]);

}

@Override
public void onResume(){
    super.onResume();

    // Controlla qual e il colore di sfondo nei settings e lo applica
    FrameLayout ll = (FrameLayout)findViewById(R.id.container);

    SharedPreferences sharedPref = PreferenceManager.getDefaultSharedPreferences(this);
    int bgc = Color.parseColor(sharedPref.getString("background_color", "#000000"));

    if(bgc == Color.BLACK){
        TextView myTextView = (TextView)findViewById(R.id.question);
        TextView r = (TextView)findViewById(R.id.answer);
        myTextView.setTextColor(Color.WHITE);
        r.setTextColor(Color.GRAY);
    }

    ll.setBackgroundColor(bgc);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {

    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.game, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}


public void trueAnswer(View view){

    if(info[2] == "1"){

        // Create new fragment and transaction
        FragmentCorrect newFragment = new FragmentCorrect();
        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();

        // Replace whatever is in the fragment_container view with this fragment,
        // and add the transaction to the back stack
        transaction.replace(R.id.container, newFragment);

        // Commit the transaction
        transaction.commit();

        newFragment.changeText(info[1], info[0]);

    }else{

        // Create new fragment and transaction
        FragmentWrong newFragment = new FragmentWrong();
        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();

        // Replace whatever is in the fragment_container view with this fragment,
        // and add the transaction to the back stack
        transaction.replace(R.id.container, newFragment);

        // Commit the transaction
        transaction.commit();

        newFragment.changeText(info[1], info[0]);
    }

}

public void falseAnswer(View view){

    if(info[2] == "1"){

        // Create new fragment and transaction
        FragmentCorrect newFragment = new FragmentCorrect();
        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();

        // Replace whatever is in the fragment_container view with this fragment,
        // and add the transaction to the back stack
        transaction.replace(R.id.container, newFragment);

        // Commit the transaction
        transaction.commit();

        newFragment.changeText(info[1], info[0]);

    }else{

        // Create new fragment and transaction
        FragmentWrong newFragment = new FragmentWrong();
        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();

        // Replace whatever is in the fragment_container view with this fragment,
        // and add the transaction to the back stack
        transaction.replace(R.id.container, newFragment);

        // Commit the transaction
        transaction.commit();

        newFragment.changeText(info[1], info[0]);
    }

}

/**
 * A placeholder fragment containing a simple view.
 */
public static class PlaceholderFragment extends Fragment {

    public PlaceholderFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_game, container,
                false);
        return rootView;
    }
}

}

FragmentCorrect：

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class FragmentCorrect extends Fragment {

TextView questionTv, answerTv;

public FragmentCorrect() {
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_corretto, container,
            false);

    questionTv = (TextView)rootView.findViewById(R.id.question);
    answerTv = (TextView)rootView.findViewById(R.id.answer);

    return rootView;
}

public void changeText(String question, String answer){
    questionTv.setText(question);
    answerTv.setText(answer);
}

}

FragmentWrong：（与FragmentCorrect相同的代码，但具有不同的片段布局）。

logcat的：

05-19 12:13:04.278: E/AndroidRuntime(16694): FATAL EXCEPTION: main
05-19 12:13:04.278: E/AndroidRuntime(16694): java.lang.IllegalStateException: Could not execute method of the activity
05-19 12:13:04.278: E/AndroidRuntime(16694):    at android.view.View$1.onClick(View.java:3704)
05-19 12:13:04.278: E/AndroidRuntime(16694):    at android.view.View.performClick(View.java:4232)
05-19 12:13:04.278: E/AndroidRuntime(16694):    at android.view.View$PerformClick.run(View.java:17298)
05-19 12:13:04.278: E/AndroidRuntime(16694):    at android.os.Handler.handleCallback(Handler.java:615)
05-19 12:13:04.278: E/AndroidRuntime(16694):    at android.os.Handler.dispatchMessage(Handler.java:92)
05-19 12:13:04.278: E/AndroidRuntime(16694):    at android.os.Looper.loop(Looper.java:137)
05-19 12:13:04.278: E/AndroidRuntime(16694):    at android.app.ActivityThread.main(ActivityThread.java:4921)
05-19 12:13:04.278: E/AndroidRuntime(16694):    at java.lang.reflect.Method.invokeNative(Native Method)
05-19 12:13:04.278: E/AndroidRuntime(16694):    at java.lang.reflect.Method.invoke(Method.java:511)
05-19 12:13:04.278: E/AndroidRuntime(16694):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1027)
05-19 12:13:04.278: E/AndroidRuntime(16694):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:794)
05-19 12:13:04.278: E/AndroidRuntime(16694):    at dalvik.system.NativeStart.main(Native Method)
05-19 12:13:04.278: E/AndroidRuntime(16694): Caused by: java.lang.reflect.InvocationTargetException
05-19 12:13:04.278: E/AndroidRuntime(16694):    at java.lang.reflect.Method.invokeNative(Native Method)
05-19 12:13:04.278: E/AndroidRuntime(16694):    at java.lang.reflect.Method.invoke(Method.java:511)
05-19 12:13:04.278: E/AndroidRuntime(16694):    at   android.view.View$1.onClick(View.java:3699)
05-19 12:13:04.278: E/AndroidRuntime(16694):    ... 11 more
05-19 12:13:04.278: E/AndroidRuntime(16694): Caused by: java.lang.NullPointerException
05-19 12:13:04.278: E/AndroidRuntime(16694):    at    com.example.quizone_2.FragmentWrong.changeText(FragmentWrong.java:29)
05-19 12:13:04.278: E/AndroidRuntime(16694):    at com.example.quizone_2.GameActivity.trueAnswer(GameActivity.java:151)
05-19 12:13:04.278: E/AndroidRuntime(16694):    ... 14 more
05-19 12:13:06.403: I/Process(16694): Sending signal. PID: 16694 SIG: 9

非常感谢您提前

Answer 1

您正在创建一个新片段，并立即在其上调用changeText()。创建片段视图，调用生命周期回调（如onCreateView()）的片段事务尚未运行。

考虑使用bundle将参数传递给fragmens，而不是直接在片段生命周期之外调用片段方法。

Answer 2

您正在致电

newFragment.changeText(info[1], info[0]);

太快了。您需要等到片段附加到Activity。您的观点为空。

还可以使用.equals来比较字符串而不是==。

if(info[2].equals("1"))

了解片段生命周期

http://developer.android.com/guide/components/fragments.html

进一步添加laalto发布的内容

Send data from activity to fragment in android

Android - IllegalStateException：无法执行活动的方法

2 个答案: