Android 启动 Intent 并在 TextView 中使用 setText() 后应用崩溃

Question

我正在尝试在已启动的 activity 中使用 TextView 中的意图和设置值来启动 activity，但是当我尝试这样做时，我的应用程序崩溃了。这是我要启动的 activity。当我尝试在最后两行代码中设置文本时它崩溃了

public class GameOver extends Activity {

  TextView correctTxt;
  TextView incorrectTxt;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);

      Intent intent = getIntent();
      int correct = intent.getIntExtra("correct", 0);
      int incorrect = intent.getIntExtra("incorrect", 0);

      correctTxt = (TextView)findViewById(R.id.correct_txt);
      incorrectTxt = (TextView)findViewById(R.id.incorrect_txt);

      correctTxt.setText("" + correct);
      incorrectTxt.setText("" + incorrect);
  }
}

以及正在启动的 activity。我在 trueButton onClickListener 方法中使用了意图：

package com.example.beithia.geotest;

import android.app.Activity;
import java.util.*;

import android.content.Intent;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
import android.content.Intent;


public class TestActivity extends Activity {

  private Button trueButton;
  private Button falseButton;
  private TextView questionTextView;
  private TextView correctNum;
  private TextView incorrectNum;
  private TextView avgScore;
  int numOfCorrect = 0;
  int numOfIncorrect = 0;
  double num = 1;

  private TrueFalse[] questionBank = new TrueFalse[] {
    new TrueFalse(R.string.question_oceans, true),
    new TrueFalse(R.string.question_mideast, false),
    new TrueFalse(R.string.question_americas, true),
    new TrueFalse(R.string.question_asia,true),
    new TrueFalse(R.string.question_channel_islands,true),
    new TrueFalse(R.string.question_china,false),
    new TrueFalse(R.string.question_mexico,true),
    new TrueFalse(R.string.question_turkey,false),
    new TrueFalse(R.string.question_everest,false),
    new TrueFalse(R.string.question_colombia,false),
    new TrueFalse(R.string.question_vatican,true),
    new TrueFalse(R.string.question_nile,true),
  };

  private int currentIndex = 0;

  private void updateQuestion() {
    int question = questionBank[currentIndex].getQuestion();
    questionTextView.setText(question);
  }

  private void checkAnswer(boolean userPressedTrue) {
    boolean answerIsTrue = questionBank[currentIndex].isTrueQuestion();
    int msgId = 0;
    if (userPressedTrue == answerIsTrue) {
        msgId = R.string.correct_toast;
        numOfCorrect++;
    }
    else {
        msgId = R.string.incorrect_toast;
        numOfIncorrect++;
    }
    Toast.makeText(this,msgId,Toast.LENGTH_SHORT).show();
  }


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

    questionTextView = (TextView)findViewById(R.id.question_text_view);
    correctNum = (TextView)findViewById(R.id.correct_num);
    incorrectNum = (TextView)findViewById(R.id.incorrect_num);
    avgScore = (TextView)findViewById(R.id.average_score);


    trueButton = (Button) findViewById(R.id.true_button);
    trueButton.setOnClickListener(new View.OnClickListener() {
      @Override
      public void onClick(View v) {
          checkAnswer(true);
          double score = (numOfCorrect / num) * 100;
          currentIndex = (currentIndex + 1) % questionBank.length;
          correctNum.setText("Correct: " + numOfCorrect);
          incorrectNum.setText("Incorrect: " + numOfIncorrect);
          avgScore.setText("Score: " + String.format("%.2f", score) + "%");
          updateQuestion();
          num++;
          if(num > 10) {
            Intent intent = new Intent(TestActivity.this, GameOver.class);
            intent.putExtra("correct", numOfCorrect);
            intent.putExtra("incorrect", numOfIncorrect);
            startActivity(intent);
          }

      }

    });
    falseButton = (Button) findViewById(R.id.false_button);
    falseButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
          checkAnswer(false);
          double score = (numOfCorrect / num) * 100;
          currentIndex = (currentIndex + 1) % questionBank.length;
          correctNum.setText("Correct: " + numOfCorrect);
          incorrectNum.setText("Incorrect: " + numOfIncorrect);
          avgScore.setText("Score: " + String.format("%.2f", score) + "%");
          updateQuestion();
          num++;

        }

    });

    updateQuestion();
  }
}

这是 activity_main.xml 的布局：

    <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:id="@+id/correct_num"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textColor="#ff00ff12" />

    <TextView
        android:id="@+id/incorrect_num"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textColor="#ffff5440" />

    <TextView
        android:id="@+id/average_score"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textColor="#ffff8c1a" />

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



    <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>

以及 activity_game_over.xml 的布局：

    <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:id="@+id/correct_txt"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>

   <TextView
       android:id="@+id/incorrect_txt"
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"/>

    </LinearLayout>

如果我使用 setContentView(R.layout.activity_game_over); 我可以让它工作然而，当我再次尝试启动主 activity 时，它会启动 GameOver Activity，但它应该启动 GeoQuiz activity。

Answer 1

在 GameOver activity 中您没有设置任何内容视图 setContentView()，因此找不到您的 textView，findViewById returns null，因此在调用 setText().

时会出现 NullPointerException

Answer 2

I can get it to work if I use the setContentView(R.layout.activity_game_over); however when I try to launch the main activity again it starts the GameOver Activity, but it should start the GeoQuiz activity instead. Please help!

启动时运行的 activity 在项目的 android 清单 xml 文件中定义。

寻找动作 android:name="android.intent.action.MAIN"

Android 启动 Intent 并在 TextView 中使用 setText() 后应用崩溃

Android app crashes after launching intent and using setText() in TextView

java

crash

android

android-intent