单击返回按钮时应用程序崩溃

Question

我正在尝试将值K从活动A传递到B.当button单击活动B中的保存时,它将再次将值k传递给活动A. 但如果我想返回A,应用程序崩溃了.

活动A中的一些代码片段

     public void onClick(DialogInterface dialog, int item) {
                    if (item == 0) {
                        Intent intent = new Intent(getActivity().getApplicationContext(), Project1.class);
                       intent.putExtra("k",k);
                        startActivityForResult(intent, 0);
                    } else if (item == 1) {
                        Intent intent = new Intent(getActivity().getApplicationContext(), Petrol.class);
                       intent.putExtra("k", k);
                        startActivityForResult(intent, 1);
                    }

 public void onActivityResult(int requestCode, int resultCode, Intent data) {
        int button = data.getIntExtra("k1", 0);
        if (button == 1) {
            switch (requestCode) {
                case 0:
                    String result = data.getStringExtra("text");
                    String b = data.getStringExtra("a");
                     as=Long.parseLong(result);
                    c.setText("            " + b + "------" + "RM " + result);
                    break;

                case 1:
                    String result1 = data.getStringExtra("text");
                    String b1 = data.getStringExtra("a");
                     as1=Long.parseLong(result1);
                    c.setText("            " + b1 + "------" + "RM " + result1);
                    break;
            }
        }
        else if(button==2)
        {
            switch (requestCode) {
                case 0:
                    String result = data.getStringExtra("text");
                    String b = data.getStringExtra("a");
                     bs=Long.parseLong(result);
                    d.setText("            " + b + "------" + "RM " + result);
                    break;

                case 1:
                    String result1 = data.getStringExtra("text");
                    String b1 = data.getStringExtra("a");
                     bs1=Long.parseLong(result1);
                    d.setText("            " + b1 + "------" + "RM " + result1);
                    break;
            }

        }

活动B.

  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.project);
   txt= (EditText)findViewById(R.id.editText36);
    Button b=(Button)findViewById(R.id.button17);

    b.setOnClickListener(new View.OnClickListener() {
        public void onClick(View arg0) {
            Intent returnIntent = new Intent();
            a="Project";
            text = txt.getText().toString();
            returnIntent.putExtra("text", text);
            returnIntent.putExtra("a", a);
            final int k1 = getIntent().getExtras().getInt("k");
            returnIntent.putExtra("k1", k1);
            setResult(Activity.RESULT_OK, returnIntent);
            finish();
        }
    });

}

@Override
public void onBackPressed()
{
    Intent intent = new Intent(Project1.this, Claims.class);
    startActivity(intent);
    finish();
}

LogCat错误

10-28 15:55:26.612    3641-3641/com.example.project.project E/AndroidRuntime? FATAL EXCEPTION: main
    Process: com.example.project.project, PID: 3641
    java.lang.RuntimeException: Failure delivering result ResultInfo{who=android:fragment:0, request=2, result=0, data=null} to activity {com.example.project.project/com.example.project.project.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'int android.content.Intent.getIntExtra(java.lang.String, int)' on a null object reference

最新错误

 10-28 16:54:56.150    6381-6381/com.example.project.project E/AndroidRuntime? FATAL EXCEPTION: main
    Process: com.example.project.project, PID: 6381
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.project.project/com.example.project.project.Claims}: java.lang.ClassCastException: com.example.project.project.Claims cannot be cast to android.app.Activity
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2327)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
            at android.app.ActivityThread.-wrap11(ActivityThread.java)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:148)

我确实喜欢@we是borg建议并在mainfest.xml中声明活动A(claims.java),但是得到上面的错误

谢谢大家......我确实喜欢这个,它解决了:)

活动A 声明 public static final int CAMERA_REQUEST_CODE = 6; 添加else if(requestCode==CAMERA_REQUEST_CODE) {}after else if(button==5){}

活动B.

使用

@Override
    public void onBackPressed()
    {
        Intent returnIntent = new Intent();
        setResult(Activity.RESULT_CANCELED, returnIntent);
        finish();
    }

而不是@Override

 public void onBackPressed()
    {
        Intent intent = new Intent(Project1.this, Claims.class);
        startActivity(intent);
        finish();
    }

Answer 1

按后退按钮时,默认结果代码为RESULT_CANCEL,返回意图为空.

您需要在onActivityResult中检查它,或在活动B中覆盖onBackPressed方法并设置必要的结果值.

编辑:

以下列方式覆盖onBackPressed(活动B)

@Override
public void onBackPressed() {
    Intent returnIntent = new Intent();
    a="Project";
    text = txt.getText().toString();
    returnIntent.putExtra("text", text);
    returnIntent.putExtra("a", a);
    final int k1 = getIntent().getExtras().getInt("k");
    returnIntent.putExtra("k1", k1);
    setResult(Activity.RESULT_OK, returnIntent);
    super.onBackPressed();
}

在这种情况下,您将发回必要的结果值.

如果您不想在按下后退按钮上发送任何值,则可以在onActivityResult中检查结果代码

public void onActivityResult(int requestCode, int resultCode, Intent data) {
    // int button = data.getIntExtra("k1", 0); // data could be null. and here you are getting NullPointerException
    // if (button == 1) {
    switch (requestCode) {
        case 0:
            if (resultCode == RESULT_OK) {
                 String result = data.getStringExtra("text");
                String b = data.getStringExtra("a");
                as=Long.parseLong(result);
                c.setText("            " + b + "------" + "RM " + result);
            } else if (resultCode == RESULT_CANCEL) {
                // TODO other functionality - when you do not override onBackPressed in activity B
            }
            break;
            ...

    }
}