从第一个活动到第二个活动的返回按钮使应用程序崩溃

Question

好的，这就是我的问题，我有两个活动，它们都用于输入信息。 一个导致另一个。 当我在第二个活动中按下返回按钮时，应用程序崩溃了，我也不知道为什么。

这是第一个活动的代码：

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();
                }
            }
        });
    }
}

这是第二个活动的代码：

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();
        }
    }
}

这是暗恋发生时的日志猫：

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) 

Answer 1

您要两次调用startActivity ，一次是在放置Extras之后，一次是在Extras之后。

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

通过这种方式，您实际上可以在将其他内容实际放入Intent 之前开始活动。 只需删除第一个电话，然后将其保留为：

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

这只是一条建议：用小写字母命名变量并使用驼峰式大小写（这不是Add_Comment_Picture ，而是将其命名为addCommentPictureIntent ）是一种常规约定。 最后，还可以将其表示的类型连接起来，这是区分变量的好方法。 您可以在线阅读有关约定的更多信息，但遵循它们对于使代码更具可读性很有用。

Answer 2

它是NPE因此我建议您一次查看什么是空指针异常以及如何解决它，以更好地了解NPE 。

在您的情况下， bundle为null意味着您正尝试从null对象访问String 。 因此，始终最好习惯在访问之前先检查getIntent().getExtras()是否为null ，以防止崩溃

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

或要预先检查特定密钥，您可以这样做，

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");
         ...
       }
  }

Answer 3

使用下面的代码（您的问题是您在放入附加内容之前开始活动）：

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();
            }
        }
    });
}
}