Question

我遇到了这个错误：当我按下一个按钮时，它会进入一个有阵列的活动。在添加阵列之前，它很好。添加数组后，应用程序崩溃。

public class navigation_front extends AppCompatActivity {
    Button scan_btn;
    Spinner dest;
    EditText Edit_current;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(navigation_front);
        scan_btn = (Button) findViewById(R.id.scan_btn);
        final Activity activity = this;
        scan_btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                IntentIntegrator integrator = new IntentIntegrator(activity);
                integrator.setDesiredBarcodeFormats(IntentIntegrator.PRODUCT_CODE_TYPES);
                integrator.setPrompt("Scan");
                integrator.setCameraId(0);
                integrator.setBeepEnabled(false);
                integrator.setBarcodeImageEnabled(false);
                integrator.initiateScan();

            }
        });
        dest = (Spinner) findViewById(R.id.edit_destination);
        String edit_destination = dest.getSelectedItem().toString().trim();
        final ArrayAdapter adapter = ArrayAdapter.createFromResource(this, R.array.destination_array, R.layout.support_simple_spinner_dropdown_item);
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        dest.setAdapter(adapter);
        dest.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                String type = parent.getItemAtPosition(position).toString();
            }

            @Override
            public void onNothingSelected(AdapterView<?> parent) {
            }
        });
    }

    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        IntentResult result = IntentIntegrator.parseActivityResult(requestCode, resultCode, data);
        if(result.getContents() != null){
            if(result.getContents() == null) {
                Log.d("MainActivity", "Cancelled scan");
                Toast.makeText(this, "Cancelled", Toast.LENGTH_LONG).show();
            } else {
                EditText editText =(EditText)findViewById(R.id.Edit_current);
                editText.setText("" + result.getContents(), TextView.BufferType.EDITABLE);
            }

        }

以下是错误日志：

FATAL EXCEPTION: main
                  Process: com.sp.ez_mart, PID: 15263
                  java.lang.RuntimeException: Unable to start activity ComponentInfo{com.sp.ez_mart/com.sp.ez_mart.navigation_front}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2726)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2787)
                      at android.app.ActivityThread.-wrap12(ActivityThread.java)
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1504)
                      at android.os.Handler.dispatchMessage(Handler.java:102)
                      at android.os.Looper.loop(Looper.java:154)
                      at android.app.ActivityThread.main(ActivityThread.java:6247)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:872)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:762)
                   Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference
                      at com.sp.ez_mart.navigation_front.onCreate(navigation_front.java:54)
                      at android.app.Activity.performCreate(Activity.java:6754)
                      at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2679)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2787) 
                      at android.app.ActivityThread.-wrap12(ActivityThread.java) 
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1504) 
                      at android.os.Handler.dispatchMessage(Handler.java:102) 
                      at android.os.Looper.loop(Looper.java:154) 
                      at android.app.ActivityThread.main(ActivityThread.java:6247) 
                      at java.lang.reflect.Method.invoke(Native Method) 
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:872) 
                      at

com.android.internal.os.ZygoteInit.main（ZygoteInit.java:762）

Answer 1

可能

String type = parent.getItemAtPosition(position).toString();

由于parent.getItemAtPosition(position)返回null而导致问题。

使用Spinner从position获取所选项目，并将数据源传递给ArrayAdapter构造函数：

@Override
public void onItemSelected(AdapterView<?> parent,View view,int position,long id) {
  // get Array from xml 
  String [] dataArray = getResources().getStringArray(R.array.destination_array);
  String type = dataArray[position];
}

Answer 2

用@ρяσѕρєя解决了它添加了K行并删除了一些行

public class navigation_front extends AppCompatActivity {
    Button scan_btn;
    Spinner dest;
    EditText Edit_current;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(navigation_front);
        scan_btn = (Button) findViewById(R.id.scan_btn);
        final Activity activity = this;
        scan_btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                IntentIntegrator integrator = new IntentIntegrator(activity);
                integrator.setDesiredBarcodeFormats(IntentIntegrator.PRODUCT_CODE_TYPES);
                integrator.setPrompt("Scan");
                integrator.setCameraId(0);
                integrator.setBeepEnabled(false);
                integrator.setBarcodeImageEnabled(false);
                integrator.initiateScan();

            }
        });
        dest = (Spinner) findViewById(R.id.edit_destination);
        final ArrayAdapter adapter = ArrayAdapter.createFromResource(this, R.array.destination_array, R.layout.support_simple_spinner_dropdown_item);
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        dest.setAdapter(adapter);
        dest.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                String [] dataArray = getResources().getStringArray(R.array.destination_array);
                String type = dataArray[position];}

            @Override
            public void onNothingSelected(AdapterView<?> parent) {
            }
        });
    }

    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        IntentResult result = IntentIntegrator.parseActivityResult(requestCode, resultCode, data);
        if(result.getContents() != null){
            if(result.getContents() == null) {
                Log.d("MainActivity", "Cancelled scan");
                Toast.makeText(this, "Cancelled", Toast.LENGTH_LONG).show();
            } else {
                EditText editText =(EditText)findViewById(R.id.Edit_current);
                editText.setText("" + result.getContents(), TextView.BufferType.EDITABLE);
            }

        }


    }
}

尝试调用null对象错误

2 个答案: