BigNerdRanch android教程，geoquiz中的ClassCast异常

时间：2015-05-15 06:49:08

标签： android

真的无法找出bug的位置。按下＆＃34;作弊时，应用程序崩溃了＃34;按钮（开始第二个活动）。 抛出转发异常

GeoQuizActivity.java：

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package com.bignerdranch.android.quiz;


import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageButton;
import android.widget.TextView;
import android.widget.Toast;



public class GeoQuizActivity extends Activity {
    /** Called when the activity is first created. */
	private static final String TAG = "GeoQuizActivity";
	private static final String KEY_INDEX ="index";
   private Button mTrueButton;
   private Button mFalseButton;
   private Button mCheatButton;
   private ImageButton mNextButton;
   private ImageButton mPrevButton;
   private TextView mQuestionTextView;
   private boolean mIsCheater;
   
   private void updateQuestion(){
	   int question = mQuestionBank[mCurrentIndex].getQuestion();
		mQuestionTextView.setText(question);
   }
   private void checkAnswer(boolean userPressedTrue){
	   boolean answerIsTrue = mQuestionBank[mCurrentIndex].isTrueQuestion();
	   int messageResId = 0;
	   if(mIsCheater){
		   messageResId=R.string.judgment_toast;
	   }
	   else{
		   if (userPressedTrue==answerIsTrue){
			   messageResId =R.string.correct_toast;
		   } else{
			   messageResId = R.string.incorrect_toast;
		   }
		   Toast.makeText(this, messageResId, Toast.LENGTH_SHORT).show();
	   }
   }
   @Override
   protected void onActivityResult(int requestCode, int resultCode, Intent data){
	   if(data==null){
		   return;
	   }
	   mIsCheater = data.getBooleanExtra(CheatActivity.EXTRA_ANSWER_SHOWN, false);
   }
   private TrueFalse [] mQuestionBank = new TrueFalse[] {
		   new TrueFalse(R.string.question_oceans, true),
		   new TrueFalse(R.string.question_mideast, false),
		   new TrueFalse(R.string.question_africa, false),
		   new TrueFalse(R.string.question_americas, true),
		   new TrueFalse(R.string.question_asia, true),
   };
   private int mCurrentIndex = 0;
	@Override
    public void onCreate(Bundle savedInstanceState) {
		Log.d(TAG, "OnCreate(Bundle) called");
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        if(savedInstanceState != null){
        	mCurrentIndex = savedInstanceState.getInt(KEY_INDEX, 0);
        }
        mQuestionTextView = (TextView)findViewById(R.id.question_text_view);
        mQuestionTextView.setOnClickListener(new View.OnClickListener(){
        	@Override
        	public void onClick(View v){
        		mCurrentIndex=(mCurrentIndex+1)%mQuestionBank.length;
        		updateQuestion();
        	}
        });
        
        mTrueButton = (Button)findViewById(R.id.true_button);
        mTrueButton.setOnClickListener(new View.OnClickListener(){
        	@Override
        	public void onClick (View v){
        		checkAnswer(true);
        		    			
        		}
        	});
        
        mFalseButton = (Button)findViewById(R.id.false_button);
        mFalseButton.setOnClickListener(new View.OnClickListener(){
        	@Override
        	public void onClick (View v){
        		checkAnswer(false);
        	}
        	});
        mNextButton =(ImageButton)findViewById(R.id.next_button);
        mNextButton.setOnClickListener(new View.OnClickListener(){
        	@Override
        	public void onClick (View v){
        		mCurrentIndex= (mCurrentIndex+1)%mQuestionBank.length;
        		updateQuestion();
        		mIsCheater=false;
        	}
        });
        mPrevButton = (ImageButton)findViewById(R.id.prev_button);
        mPrevButton.setOnClickListener(new View.OnClickListener(){
        	@Override
        	public void onClick(View v){
        		if(mCurrentIndex==0){
        			mCurrentIndex=mQuestionBank.length-1;
        			
        		}
        		else{
        		mCurrentIndex=(mCurrentIndex-1);
        		
        		}
        		updateQuestion();
        		mIsCheater=false;
        	
        }
        });
        mCheatButton = (Button)findViewById(R.id.cheat_button);
        mCheatButton.setOnClickListener(new View.OnClickListener() {
        				
			@Override
			public void onClick(View v) {
				Intent i = new Intent(GeoQuizActivity.this, CheatActivity.class);
				boolean answerIsTrue = mQuestionBank[mCurrentIndex].isTrueQuestion();
				i.putExtra(CheatActivity.EXTRA_ANSWER_IS_TRUE, answerIsTrue);
				startActivityForResult(i, 0);
								
			}
		});
        
        		
        updateQuestion();
        
        }
	@Override
	public void onSaveInstanceState(Bundle savedInstanceState){
		super.onSaveInstanceState(savedInstanceState);
		Log.i(TAG, "onSaveInstanceState");
		savedInstanceState.putInt(KEY_INDEX, mCurrentIndex);
	}
	@Override
	public void onStart(){
		super.onStart();
		Log.d(TAG, "onStart() called");
		}
	@Override
	public void onPause(){
		super.onPause();
		Log.d(TAG, "onPause() called");
	}
	
	@Override
	public void onResume(){
		super.onResume();
		Log.d(TAG, "onResume() called");
	}
	@Override
	public void onStop(){
		super.onStop();
		Log.d(TAG, "onStop() called");
	}
	@Override
	public void onDestroy(){
		super.onDestroy();
		Log.d(TAG, "onDestroy() called");
	}
}
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cheatActivity.java：

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package com.bignerdranch.android.quiz;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class CheatActivity extends Activity {
	private boolean mAnswerIsTrue;
	private TextView mAnswerTextView;
	private Button mShowAnswer;
	public static final String EXTRA_ANSWER_IS_TRUE = "com.bignerdranch.android.quiz.answer_is_true";
	public static final String EXTRA_ANSWER_SHOWN = "com.bignerdranch.android.quiz.answer_shown";
	private void setAnswerShownResult(boolean isAnswerShown){
		Intent data = new Intent();
		data.putExtra(EXTRA_ANSWER_SHOWN, isAnswerShown);
		setResult(RESULT_OK, data);
	}
	
@Override
protected void onCreate(Bundle savedInstanceState){
	super.onCreate(savedInstanceState);
	setContentView(R.layout.activity_cheat);
	mAnswerIsTrue = getIntent().getBooleanExtra(EXTRA_ANSWER_IS_TRUE, true);
	mAnswerTextView = (TextView)findViewById(R.id.answerTextView);
	mShowAnswer = (Button)findViewById(R.id.showAnswerButton);
	setAnswerShownResult(false);
	mShowAnswer.setOnClickListener(new View.OnClickListener() {
		
		@Override
		public void onClick(View v) {
			if(mAnswerIsTrue){
				mAnswerTextView.setText(R.string.true_button);
			}
			else{
				mAnswerTextView.setText(R.string.false_button);
			}
			setAnswerShownResult(true);
			
			
		}
	});
}
}
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main.xml

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<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
android:orientation="vertical" >

<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:padding="24dp"
android:id="@+id/question_text_view" />
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal" >
<Button
    android:id="@+id/true_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/true_button" />
<Button
    android:id="@+id/false_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/false_button" />
</LinearLayout>
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal">
<ImageButton
android:id="@+id/prev_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:contentDescription="@string/prev_button"
android:src="@drawable/arrow_left"
/>
<ImageButton
android:id="@+id/next_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:contentDescription="@string/next_button" 
android:src="@drawable/arrow_right"
/>
<Button 
android:id="@+id/cheat_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/cheat_button"/>

</LinearLayout>
</LinearLayout>
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<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" 
    android:gravity="center">
    
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:padding="24dp"
android:text="@string/warning_text"/>

<TextView 
android:id="@+id/answerTextView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:padding="24dp"/>

<TextView
android:id="@+id/showAnswerButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/show_answer_button"/>
    
</LinearLayout>
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谢谢！

编辑：logCat： 我从顶部第3行开始t know which line causes the exception or how to find it. In logCat, it s。

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05-15 15:32:57.116: W/dalvikvm(349): threadid=1: thread exiting with uncaught exception (group=0x40015560)
05-15 15:32:57.256: E/AndroidRuntime(349): FATAL EXCEPTION: main
05-15 15:32:57.256: E/AndroidRuntime(349): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.bignerdranch.android.quiz/com.bignerdranch.android.quiz.CheatActivity}: java.lang.ClassCastException: android.widget.TextView
05-15 15:32:57.256: E/AndroidRuntime(349): 	at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
05-15 15:32:57.256: E/AndroidRuntime(349): 	at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
05-15 15:32:57.256: E/AndroidRuntime(349): 	at android.app.ActivityThread.access$1500(ActivityThread.java:117)
05-15 15:32:57.256: E/AndroidRuntime(349): 	at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
05-15 15:32:57.256: E/AndroidRuntime(349): 	at android.os.Handler.dispatchMessage(Handler.java:99)
05-15 15:32:57.256: E/AndroidRuntime(349): 	at android.os.Looper.loop(Looper.java:123)
05-15 15:32:57.256: E/AndroidRuntime(349): 	at android.app.ActivityThread.main(ActivityThread.java:3683)
05-15 15:32:57.256: E/AndroidRuntime(349): 	at java.lang.reflect.Method.invokeNative(Native Method)
05-15 15:32:57.256: E/AndroidRuntime(349): 	at java.lang.reflect.Method.invoke(Method.java:507)
05-15 15:32:57.256: E/AndroidRuntime(349): 	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
05-15 15:32:57.256: E/AndroidRuntime(349): 	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
05-15 15:32:57.256: E/AndroidRuntime(349): 	at dalvik.system.NativeStart.main(Native Method)
05-15 15:32:57.256: E/AndroidRuntime(349): Caused by: java.lang.ClassCastException: android.widget.TextView
05-15 15:32:57.256: E/AndroidRuntime(349): 	at com.bignerdranch.android.quiz.CheatActivity.onCreate(CheatActivity.java:28)
05-15 15:32:57.256: E/AndroidRuntime(349): 	at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
05-15 15:32:57.256: E/AndroidRuntime(349): 	at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
05-15 15:32:57.256: E/AndroidRuntime(349): 	... 11 more
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1 个答案:

答案 0 :(得分：0)

Logcat是你的朋友：

...
at com.bignerdranch.android.quiz.CheatActivity.onCreate(CheatActivity.java:28) 
...

显然，您正在尝试将某个对象投射到某个类别，而该类别无法从中分配。检查CheatActivity.java，第28行。

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