Question

我从另一个类里面的类调用startActivityForResult（）时遇到问题（Null Pointer Exception），这里是代码：

public class OCRActivity extends Activity {

public OCRActivity(String operator)
{
    this.operator = operator;
}


public void startCameraActivity() {

    final Intent capture_intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
    startActivityForResult(capture_intent, 1); // I get the Null pointer Exception here
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {

    if (resultCode == RESULT_OK) {

        if(requestCode == 1){
            //get the Uri for the captured image
            picUri = data.getData();
            //carry out the crop operation
            performCrop();
        }
}

这是我拨打startCameraActivity()

的地方

public class WayToFillActivity extends Activity implements OnClickListener {

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.way_to_fill);

    CAMERA_BTN = (Button) findViewById(R.id.camera_btn);
    CAMERA_BTN.setOnClickListener(this);
    Intent operator_intent =  getIntent();
    OPERATOR = operator_intent.getStringExtra("operator");
}

@Override
public void onClick(View v) {
    if (v.getId() == R.id.camera_btn)
    {
        OCRActivity ocr = new OCRActivity(OPERATOR);
        ocr.startCameraActivity();

    }

}

所以请告诉我，如果我做错了什么!!

Logcat

01-13 16:22:26.583: E/AndroidRuntime(32425): java.lang.NullPointerException
01-13 16:22:26.583: E/AndroidRuntime(32425):    at     android.app.Activity.startActivityForResult(Activity.java:3190)
01-13 16:22:26.583: E/AndroidRuntime(32425):    at com.almannaa.EasyRecharge.OCRActivity.startCameraActivity(OCRActivity.java:176)

Answer 1

您将OCRActivity视为普通的Java类，而不是另一个Activity。因此，当您致电startActivityForResult()时，您会收到一个NPE，因为尚未调用活动的onCreate()，这意味着其当前实例无法调用startActivityForResult()

相反，请尝试使用：

public class WayToFillActivity extends Activity implements OnClickListener {

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.way_to_fill);

    CAMERA_BTN = (Button) findViewById(R.id.camera_btn);
    CAMERA_BTN.setOnClickListener(this);
    Intent operator_intent =  getIntent();
    OPERATOR = operator_intent.getStringExtra("operator");
}

@Override
public void onClick(View v) {
    if (v.getId() == R.id.camera_btn)
    {
        OCRActivity ocr = new OCRActivity(OPERATOR);
        ocr.startCameraActivity();

    }

}

public void startCameraActivity() {

    final Intent capture_intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
    startActivityForResult(capture_intent, 1); // I get the Null pointer Exception here
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {

    if (resultCode == RESULT_OK) {

        if(requestCode == 1){
            //get the Uri for the captured image
            picUri = data.getData();
            //carry out the crop operation
            performCrop();
        }
}
}

你应该移动像performCrop()这样的函数（以及任何其他不需要在活动本身中的函数，并且可以通过接收数据作为参数并将其返回）到单独的类中进行调用（调用它实用程序或其他）。

Answer 2

也许您应该检查数据是否为空。

@Override        
protected void onActivityResult(int requestCode, int resultCode, Intent data) {

    if (requestCode == 1 && data != null) {

        if(resultCode == RESULT_OK){
            //get the Uri for the captured image
            picUri = data.getData();
            //carry out the crop operation
            performCrop();
        } }

调用startActivityForResult（）时出现空指针异常

2 个答案: