返回按鈕從第一個活動到第二個崩潰應用程序

好的，所以這是我的問題，我有兩個活動，他們都是爲了輸入信息。一個通向另一個。當我按下返回按鈕從第二活動應用程序崩潰，我不知道爲什麼..返回按鈕從第一個活動到第二個崩潰應用程序

這是第一個活動代碼：

import android.content.Intent; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.view.View; 
import android.widget.Button; 
import android.widget.EditText; 
import android.support.design.widget.Snackbar; 

public class Add_Score extends AppCompatActivity { 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_add__score); 
     final Button Next = (Button)findViewById(R.id.buttonNext); 
     final Intent Add_Comment_Picture = new Intent(this, Add_Comment_Picture.class); 

     Next.setOnClickListener(new View.OnClickListener() { 
      public void onClick(View v) { 
       String score = ((EditText) findViewById(R.id.editText)).getText().toString(); 
       String desc = ((EditText)findViewById(R.id.editTextDesc)).getText().toString(); 
       if(score.compareTo("") != 0 && desc.compareTo("") != 0){ 
        startActivity(Add_Comment_Picture); 
        Add_Comment_Picture.putExtra("score", score); 
        Add_Comment_Picture.putExtra("desc" , desc); 
        startActivity(Add_Comment_Picture); 
       } 
       else{ 
        Snackbar.make(v , "Please fill in the score and description" , Snackbar.LENGTH_LONG).show(); 
       } 
      } 
     }); 
    } 
}

這是第二個代碼活動：

import android.Manifest; 
import android.content.Intent; 
import android.content.pm.PackageManager; 
import android.database.Cursor; 
import android.graphics.drawable.Drawable; 
import android.net.Uri; 
import android.os.Build; 
import android.provider.MediaStore; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.view.View; 
import android.widget.ImageButton; 
import android.widget.ImageView; 
import android.widget.TextView; 

import org.w3c.dom.Text; 

import java.io.File; 
import java.io.FileInputStream; 
import java.io.FileOutputStream; 
import java.io.IOException; 
import java.io.InputStream; 
import java.io.OutputStream; 
import java.text.SimpleDateFormat; 
import java.util.ArrayList; 
import java.util.Calendar; 
import java.util.Date; 
import java.util.HashMap; 
import java.util.List; 

public class Add_Comment_Picture extends AppCompatActivity { 
    static final int CAM_REQUEST = 1; 
    static final int RESULT_LOAD_IMAGE = 2; 
    ImageView imageView; 
    ImageButton button; 
    ImageButton buttonGallery; 
    String mCurrentPhotoPath; 


    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_add__comment__picture); 
     button = (ImageButton) findViewById(R.id.imageButtonCamera); 
     imageView = (ImageView) findViewById(R.id.imageView); 
     buttonGallery = (ImageButton) findViewById(R.id.imageButtonGallery_f); 


     Calendar c = Calendar.getInstance(); 

     String hours = Globals.getTimePadding(c.get(Calendar.HOUR)); 
     String minutes = Globals.getTimePadding(c.get(Calendar.MINUTE)); 
     String time = hours + ":" + minutes; 
     String value = getIntent().getExtras().getString("score"); 
     String value2 = getIntent().getExtras().getString("desc"); 
     TextView scoreText = (TextView) findViewById(R.id.textViewScore); 
     scoreText.setText("Score: " + value); 
     TextView t = (TextView) findViewById(R.id.textViewDatec); 
     t.setText(time); 
     TextView descText = (TextView) findViewById(R.id.textViewDesc); 
     descText.setText(value2); 


     button.setOnClickListener(new View.OnClickListener() { 
      public void onClick(View v) { 
       Intent camera_intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE); 
       File file = getFile(); 
       camera_intent.putExtra(MediaStore.EXTRA_OUTPUT, Uri.fromFile(file)); 
       startActivityForResult(camera_intent, CAM_REQUEST); 
      } 
     }); 

     buttonGallery.setOnClickListener(new View.OnClickListener() { 
      public void onClick(View v) { 
       Intent intent_gallery = new Intent(Intent.ACTION_PICK, MediaStore.Images.Media.EXTERNAL_CONTENT_URI); 
       startActivityForResult(intent_gallery , RESULT_LOAD_IMAGE); 
      } 
     }); 

    } 



    private String createFileName(){ 
     String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date()); 
     return "JPEG_" + timeStamp + "_.jpg"; 
    } 

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

     if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) { 

      int hasWritePermission = checkSelfPermission(Manifest.permission.WRITE_EXTERNAL_STORAGE); 
      int hasReadPermission = checkSelfPermission(Manifest.permission.READ_EXTERNAL_STORAGE); 
      int hasCameraPermission = checkSelfPermission(Manifest.permission.CAMERA); 

      List<String> permissions = new ArrayList<String>(); 
      if (hasWritePermission != PackageManager.PERMISSION_GRANTED) { 
       permissions.add(Manifest.permission.WRITE_EXTERNAL_STORAGE); 
      } 

      if (hasReadPermission != PackageManager.PERMISSION_GRANTED) { 
       permissions.add(Manifest.permission.READ_EXTERNAL_STORAGE); 
      } 

      if (hasCameraPermission != PackageManager.PERMISSION_GRANTED) { 
       permissions.add(Manifest.permission.CAMERA); 
      } 
      if (!permissions.isEmpty()) { 
       requestPermissions(permissions.toArray(new String[permissions.size()]), 111); 
      } 
     } 


    } 

    private File getFile() { 
     File folder = new File("sdcard/data/data/com.yuvaleliav1gmail.foodchain/photos"); 
     if (!folder.exists()) { 
      folder.mkdir(); 
     } 

     mCurrentPhotoPath = createFileName(); 
     File image_file = new File(folder,mCurrentPhotoPath); 
     return image_file; 
    } 

    @Override 
    protected void onActivityResult(int requestCode, int resultCode, Intent data) { 
     if(requestCode == CAM_REQUEST){ 
      copyFile("sdcard/data/data/com.yuvaleliav1gmail.foodchain/photos/" + mCurrentPhotoPath , getFilesDir().toString() + "/" + mCurrentPhotoPath); 
      File d = new File("sdcard/data/data/com.yuvaleliav1gmail.foodchain/photos/" + mCurrentPhotoPath); 
      d.delete(); 
      imageView.setImageDrawable(Drawable.createFromPath(getFilesDir().toString() + "/" + mCurrentPhotoPath)); 
     } 
     if(requestCode == RESULT_LOAD_IMAGE){ 
      if(data != null){ 
       Uri selectedImage = data.getData(); 
       String[] filePathColumn = { MediaStore.Images.Media.DATA }; 
       Cursor cursor = getContentResolver().query(selectedImage, filePathColumn, null, null, null); 
       cursor.moveToFirst(); 
       int columnIndex = cursor.getColumnIndex(filePathColumn[0]); 
       String picturePath = cursor.getString(columnIndex); 
       cursor.close(); 
       mCurrentPhotoPath = createFileName(); 
       copyFile(picturePath, getFilesDir().toString() + "/" + mCurrentPhotoPath); 
       imageView.setImageDrawable(Drawable.createFromPath(getFilesDir().toString() + "/" + mCurrentPhotoPath)); 
      } 
     } 

     super.onActivityResult(requestCode, resultCode, data); 
    } 

    @Override 
    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) { 
     switch (requestCode) { 
      case 111: { 
       for (int i = 0; i < permissions.length; i++) { 
        if (grantResults[i] == PackageManager.PERMISSION_GRANTED) { 
         System.out.println("Permissions --> " + "Permission Granted: " + permissions[i]); 


        } else if (grantResults[i] == PackageManager.PERMISSION_DENIED) { 
         System.out.println("Permissions --> " + "Permission Denied: " + permissions[i]); 

        } 
       } 
      } 
      break; 
      default: { 
       super.onRequestPermissionsResult(requestCode, permissions, grantResults); 
      } 
     } 
    } 

    public void copyFile(String path1 , String path2){ 
     InputStream inStream = null; 
     OutputStream outStream = null; 
     try{ 

      File file1 =new File(path1); 
      File file2 =new File(path2); 

      inStream = new FileInputStream(file1); 
      outStream = new FileOutputStream(file2); // for override file content 
      //outStream = new FileOutputStream(file2,<strong>true</strong>); // for append file content 

      byte[] buffer = new byte[1024]; 

      int length; 
      while ((length = inStream.read(buffer)) > 0){ 
       outStream.write(buffer, 0, length); 
      } 

      if (inStream != null)inStream.close(); 
      if (outStream != null)outStream.close(); 

      System.out.println("File Copied.."); 
     }catch(IOException e){ 
      e.printStackTrace(); 
     } 
    } 
}

這是logcat的時候暗戀發生：

05-22 12:46:50.361 8312-8312/com.yuvaleliav1gmail.foodchain E/AndroidRuntime: FATAL EXCEPTION: main 
                       Process: com.yuvaleliav1gmail.foodchain, PID: 8312 
                       java.lang.RuntimeException: Unable to start activity ComponentInfo{com.yuvaleliav1gmail.foodchain/com.yuvaleliav1gmail.foodchain.Add_Comment_Picture}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.os.Bundle.getString(java.lang.String)' on a null object reference 
                        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3253) 
                        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3349) 
                        at android.app.ActivityThread.access$1100(ActivityThread.java:221) 
                        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1794) 
                        at android.os.Handler.dispatchMessage(Handler.java:102) 
                        at android.os.Looper.loop(Looper.java:158) 
                        at android.app.ActivityThread.main(ActivityThread.java:7224) 
                        at java.lang.reflect.Method.invoke(Native Method) 
                        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
                        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120) 
                       Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.os.Bundle.getString(java.lang.String)' on a null object reference 
                        at com.yuvaleliav1gmail.foodchain.Add_Comment_Picture.onCreate(Add_Comment_Picture.java:56) 
                        at android.app.Activity.performCreate(Activity.java:6876) 
                        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1135) 
                        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3206) 
                        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3349)  
                        at android.app.ActivityThread.access$1100(ActivityThread.java:221)  
                        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1794)  
                        at android.os.Handler.dispatchMessage(Handler.java:102)  
                        at android.os.Looper.loop(Looper.java:158)  
                        at android.app.ActivityThread.main(ActivityThread.java:7224)  
                        at java.lang.reflect.Method.invoke(Native Method)  
                        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)  
                        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)

來源

2016-05-22 Yuval Eliav

可能重複[什麼是空指針異常，以及如何解決它？]（http://stackoverflow.com/questions/218384/what-is-a-null-pointer-exception-and-how-do-i-fix-it） –

使用的代碼（你的問題是你在開始活動之前就開始活動）：

public class Add_Score extends AppCompatActivity { 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_add__score); 
    final Button Next = (Button)findViewById(R.id.buttonNext); 
    final Intent Add_Comment_Picture = new Intent(this, Add_Comment_Picture.class); 

    Next.setOnClickListener(new View.OnClickListener() { 
     public void onClick(View v) { 
      String score = ((EditText) findViewById(R.id.editText)).getText().toString(); 
      String desc = ((EditText)findViewById(R.id.editTextDesc)).getText().toString(); 
      if(score.compareTo("") != 0 && desc.compareTo("") != 0){ 
       // startActivity(Add_Comment_Picture); 
       Add_Comment_Picture.putExtra("score", score); 
       Add_Comment_Picture.putExtra("desc" , desc); 
       startActivity(Add_Comment_Picture); 
      } 
      else{ 
       Snackbar.make(v , "Please fill in the score and description" , Snackbar.LENGTH_LONG).show(); 
      } 
     } 
    }); 
} 
}

來源

2016-05-22 09:59:26 pooyan

你爲什麼真的偷了我的答案，告訴我那個？ – Vucko

@Vucko對不起人。但我沒有從任何人那裏竊取任何東西。我只是回答我認爲是對的。我想你可以達到這個，如果你比較你的答案和我的答案。任何方式，我認爲「偷」這個詞是不合適的。 – pooyan

我甚至不在乎，這太糟糕了。 – Vucko

你打電話startActivity兩次，一次之前和一次後額外。

startActivity(Add_Comment_Picture); 
Add_Comment_Picture.putExtra("score", score); 
Add_Comment_Picture.putExtra("desc" , desc); 
startActivity(Add_Comment_Picture);

這樣你實際上開始活動之前，你實際上是把演員的意圖。只是刪除了第一個電話，離開它是這樣的：

Add_Comment_Picture.putExtra("score", score); 
Add_Comment_Picture.putExtra("desc" , desc); 
startActivity(Add_Comment_Picture);

這只是一個忠告：這是一個小寫字母來命名你的變量，並使用駱駝情況下（而不是Add_Comment_Picture一般慣例，你'd叫它addCommentPictureIntent）。當它們中有很多變量時，最後還要連接它所代表的類型是區分變量的好方法。您可以在線閱讀關於約定的更多信息，但它們有助於遵循並使代碼更具可讀性。

來源

2016-05-22 09:55:44 Vucko

這NPE所以我建議一次看到what-is-a-null-pointer-exception-and-how-do-i-fix-it更好地理解NPE。

在你的情況bundle是null這意味着你正在嘗試從null對象訪問String對象。因此，它總是更好的習慣，以檢查是否getIntent().getExtras()是null訪問之前，以防止崩潰像

if(getIntent().getExtras() !=null){ 
    String value = getIntent().getExtras().getString("score"); 
    String value2 = getIntent().getExtras().getString("desc"); 
    ... 
}

OR對於提前檢查特定的鍵，你可以這樣做，

Bundle extras = getIntent().getExtras(); 
if(extras != null){ 
    if (extras.containsKey("score") && extras.containsKey("desc")){ 
     String value = getIntent().getExtras().getString("score"); 
     String value2 = getIntent().getExtras().getString("desc"); 
     ... 
     } 
    }

來源

2016-05-22 09:56:15

返回按鈕從第一個活動到第二個崩潰應用程序

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