单击 return 按钮时应用程序崩溃

Question

我正在尝试将值 k 从 Activity A 传递给 B。单击 activity B 中的保存 button 时，它会将值 k 传递给 Activity又是A。但是如果我想 return 回到 A，应用程序崩溃了。

ActivityA

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;
            }

        }

ActivityB

  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 are borg 的建议，并在 mainfest.xml 中声明了 activity A (claims.java)，但出现了如上的错误

谢谢大家...我喜欢这个并且解决了:)

Activity一个 声明 public static final int CAMERA_REQUEST_CODE = 6; 添加 else if(requestCode==CAMERA_REQUEST_CODE) {}after else if(button==5){}

ActivityB

使用

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

代替@Override

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

Answer 1

在您的 class 中添加此功能：

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

我希望这是你要找的，如果不是，我会删除答案，请发表评论。

Answer 2

我认为 'null object reference' 即将到来是因为 getActivity()。检查 getActivity() 是否不返回空值，如果它不是使用上下文。或者创建一个单例对象。

Answer 3

当您按下后退按钮时，默认结果代码将为 RESULT_CANCEL 并且返回意图将为空。

您需要在 onActivityResult 中检查它或覆盖 activity B 中的方法 onBackPressed 并设置必要的结果值。

已编辑：

按以下方式覆盖 onBackPressed (activity 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时发送任何值，您可以在 onActivityResult

中查看结果代码

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;
            ...

    }
}

Answer 4

好吧，无耻地从http://developer.android.com/training/basics/intents/result.html的官方文档中复制粘贴：

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    // Check which request we're responding to
    if (requestCode == PICK_CONTACT_REQUEST) {
        // Make sure the request was successful
        if (resultCode == RESULT_OK) {
            // The user picked a contact.
            // The Intent's data Uri identifies which contact was selected.

            // Do something with the contact here (bigger example below)
        }
    }
}

确保您的代码中有 if (resultCode == RESULT_OK) 行。如果 (resultCode == RESULT_CANCELED)，则没有结果可用，Intent 为 null。

当您按下设备上的 "back" 按钮时，正常结果是取消当前 activity，因此调用 activity 得到 resultCode RESULT_CANCELED 在这种情况下，而不是通过 finish().

显式返回时设置的那个

单击 return 按钮时应用程序崩溃

App crashed when the return button is clicked

java

android

button

android-intent

onactivityresult