問題描述

在我的 android 應用程序中，我有 3 個對話框，用戶在其中將信息放入 3 個 editTexts 中，它會在隨機選擇要選擇的數據后將其中一個數據顯示到另一個類/頁面上.

In my android application , I have 3 dialogue boxes in which the user puts info into 3 editTexts and it will display the one of the data onto another class/page after it randomly picks which data to choose.

這是我的主類

public class MainActivity extends Activity {
   //Variables are displayed in this area 
    String choices[] = new String[3];
    //EditText editText;
    //EditText editText2;
    //EditText editText3;
    Button mainButton ; 

    Random rand = new Random(); 
    int finalChoice; 
    String displayChoice = ""; 
    EditText editText ; 
    EditText editText2; 
    EditText editText3;
    EditText editText4; 
    String test;
    int count = 3; 


//--------------------------- --------------------------------------------------------


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


        //Makes Button

        setContentView(R.layout.activity_main);
        declareTextBox(); 
        setButton(); 
        String choice1 = editText.getText().toString();
        String choice2 = editText2.getText().toString(); 
        String choice3 = editText3.getText().toString();

        choices[0] = choice1; //pass from click button to method.
        choices[1] = choice2;
        choices[2] = choice3;  

        finalChoice =rand.nextInt(2);


    }
     public void setButton()
     {
         final Button mainbutton = (Button) findViewById(R.id.mainButton);

         mainbutton.setOnClickListener(new View.OnClickListener() {
         public void onClick(View v) {

             test =  ((EditText) findViewById(R.id.editText4)).getText().toString(); 

        // count++; 
         //retChoice(); 
            // loadScreen(); 
         Intent i  = new Intent(MainActivity.this, resultScreen.class);
         i.putExtra("display" , displayChoice);

         Intent intent = new Intent(MainActivity.this,loadingScreen.class);

            //start the second Activity
         MainActivity.this.startActivity(intent);


          }
      }); 

     }
    public void declareTextBox()
    {
        editText = (EditText) findViewById(R.id.editText1);
        editText2 =  (EditText) findViewById(R.id.editText2); 
        editText3 = (EditText) findViewById(R.id.editText3); 

    }
    public void getString(String finalChoice)
    {
        finalChoice = displayChoice; 
    }


    public String retChoice()
    {


        displayChoice = choices[finalChoice];

        return displayChoice; 
    }
    public void clearText()
    {
         editText.setOnClickListener(new View.OnClickListener() {

                @Override
                public void onClick(View v) {
                    // TODO Auto-generated method stub

                 editText.setText(" "); 
                }
            }); 

         editText2.setOnClickListener(new View.OnClickListener() {

                @Override
                public void onClick(View v) {
                    // TODO Auto-generated method stub
                    editText2.setText(" "); 
                }
            }); 

         editText3.setOnClickListener(new View.OnClickListener() {

                @Override
                public void onClick(View v) {
                    // TODO Auto-generated method stub
                    editText3.setText(" "); 
                }
            }); 

    }
    public void getText2()
    {

    }
    public void getText()
    {



    }



    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }
}

這是我的展示類:

public class resultScreen extends Activity {
    MainActivity ma = new MainActivity(); 
    //Method supposedly retrieves the string data from MainActivity Class but somehow displayed null instead. 
    //Find a way to keep the string variable when transfering from one class to another class. 
      String finalResult = ma.retChoice(); 
      public void onCreate(Bundle resultScreen){
      super.onCreate(resultScreen);
      setContentView(R.layout.resultscreen);
      //ma.displayChoice.toString(); 

      String str = finalResult;

      TextView text = (TextView) findViewById(R.id.textView1);
      text.setText(str);

      final Button backbutton = (Button) findViewById(R.id.backButton);
      backbutton.setOnClickListener(new View.OnClickListener() {
      public void onClick(View v) 

      {

      Intent intent = new Intent(resultScreen.this,MainActivity.class);
      resultScreen.this.startActivity(intent);     


      }
        });



        }

}

這是我點擊主按鈕后的加載屏幕類

And this is my loading screen class right after the main button is clicked

public class loadingScreen extends Activity{

protected void onCreate(Bundle loadingScreen) {
    // TODO Auto-generated method stub

    super.onCreate(loadingScreen);
    setContentView(R.layout.loadingscreen);


    //If sound clip 20 sec long we don't want to carryit outside next class


    // A timer thread looking for "run" method
    Thread timer = new Thread()
    {
        public void run() {
            try {

                //this is how many mil sec
                sleep(8000);


            } catch (InterruptedException e) {
                e.printStackTrace();

            } finally {
                Intent intent = new Intent(loadingScreen.this, resultScreen.class);
                loadingScreen.this.startActivity(intent);
                loadingScreen.this.finish();

             }

        }
    };
    timer.start();
}

}

當程序嘗試在 resultScreen 上顯示數據時，我的應用程序在加載屏幕幾秒鐘后崩潰.

My app crashes a few seconds into the loading screen when the program attempts to display the data on the resultScreen.

這是我的 logCat

Here's my logCat

    05-17 22:32:54.446: D/AndroidRuntime(1181): Shutting down VM
05-17 22:32:54.446: W/dalvikvm(1181): threadid=1: thread exiting with uncaught exception (group=0x40a70930)
05-17 22:32:54.636: E/AndroidRuntime(1181): FATAL EXCEPTION: main
05-17 22:32:54.636: E/AndroidRuntime(1181): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.choiceprototest/com.example.choiceprototest.resultScreen}: java.lang.NullPointerException
05-17 22:32:54.636: E/AndroidRuntime(1181):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2106)
05-17 22:32:54.636: E/AndroidRuntime(1181):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
05-17 22:32:54.636: E/AndroidRuntime(1181):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
05-17 22:32:54.636: E/AndroidRuntime(1181):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
05-17 22:32:54.636: E/AndroidRuntime(1181):     at android.os.Handler.dispatchMessage(Handler.java:99)
05-17 22:32:54.636: E/AndroidRuntime(1181):     at android.os.Looper.loop(Looper.java:137)
05-17 22:32:54.636: E/AndroidRuntime(1181):     at android.app.ActivityThread.main(ActivityThread.java:5039)
05-17 22:32:54.636: E/AndroidRuntime(1181):     at java.lang.reflect.Method.invokeNative(Native Method)
05-17 22:32:54.636: E/AndroidRuntime(1181):     at java.lang.reflect.Method.invoke(Method.java:511)
05-17 22:32:54.636: E/AndroidRuntime(1181):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
05-17 22:32:54.636: E/AndroidRuntime(1181):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
05-17 22:32:54.636: E/AndroidRuntime(1181):     at dalvik.system.NativeStart.main(Native Method)
05-17 22:32:54.636: E/AndroidRuntime(1181): Caused by: java.lang.NullPointerException
05-17 22:32:54.636: E/AndroidRuntime(1181):     at com.example.choiceprototest.MainActivity.retChoice(MainActivity.java:101)
05-17 22:32:54.636: E/AndroidRuntime(1181):     at com.example.choiceprototest.resultScreen.<init>(resultScreen.java:18)
05-17 22:32:54.636: E/AndroidRuntime(1181):     at java.lang.Class.newInstanceImpl(Native Method)
05-17 22:32:54.636: E/AndroidRuntime(1181):     at java.lang.Class.newInstance(Class.java:1319)
05-17 22:32:54.636: E/AndroidRuntime(1181):     at android.app.Instrumentation.newActivity(Instrumentation.java:1054)
05-17 22:32:54.636: E/AndroidRuntime(1181):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2097)
05-17 22:32:54.636: E/AndroidRuntime(1181):     ... 11 more
05-17 22:33:03.385: I/Process(1181): Sending signal. PID: 1181 SIG: 9
05-17 22:33:05.435: E/Trace(1204): error opening trace file: No such file or directory (2)

謝謝各位.

推薦答案

我相信我看到了問題所在.您正在嘗試訪問您的 Array，但它是一個實例變量而不是靜態變量，因此當您退出 Activity 時它會被終止.您可以將它們放在靜態類中并以這種方式訪問??它們，也可以通過 Intent 傳遞 String 變量，具體取決于您的需要.

I believe I see the problem. You are trying to access your Array but it is an instance variable instead of static so it is being killed off when you exit your Activity. You can either put them in a static class and access them that way or pass a String variable through your Intent, depending on what you need.

如果您在離開 MainActivity 時擁有所需的 String 值，那么我可能會通過您的 Intent 傳遞它.如果該值取決于您的其他 Activity 之一中的某些內容，那么我會考慮將其放在一個單獨的類中，但看起來這不是您在這里需要的

If you have the value of the String you need when you leave MainActivity then I would probably just pass it through your Intent. If the value depended on something in one of your other Activities then I would consider putting it in a separate class but it doesn't look like that's what you need here

編輯

你已經在這里做了，有點

You are already doing it here, kind of

Intent i  = new Intent(MainActivity.this, resultScreen.class);
     i.putExtra("display" , displayChoice);

     Intent intent = new Intent(MainActivity.this,loadingScreen.class);

但是您沒有啟動會獲得 String

But you aren't starting the Activity that would get the String

i.putExtra("display" , displayChoice);

該行將傳遞一個 String 與 key "displpay" 和 displayChoice 的值，雖然我認為該值是一個空 String 在那一點上，但你沒有啟動那個 Activity.我不知道你的流程應該如何工作，但基本上你會做這樣的事情

that line would pass a String with key "displpay" and value of displayChoice, although I think that value is an empty String at that point, but you don't start that Activity. I'm lost on how your flow is suppose to work but basically you would do something like this

String displayChoice = "testValue";   // some arbitrary value--whatever you need to send
Intent i  = new Intent(MainActivity.this, resultScreen.class);  // create the Intent
i.putExtra("display" , displayChoice);  // add the extra
startActivity(i);  //start the Activity

然后在onCreate()

Intent recIntent = getIntent();  // get the Intent that started this Activity
String value = recIntent.getStringExtra("display");   // get the value using the key
// value now equals "testValue"

這篇關于EditText.getText().toString() 崩潰的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！