Android 删除时出现空指针异常\u btn

我在delete_btn收到一个空指针异常。我在下面的代码中提到了错误行，并且我被发布了相关的代码

Stacktrace:

12-22 10:03:59.897: E/AndroidRuntime(1505): FATAL EXCEPTION: main
12-22 10:03:59.897: E/AndroidRuntime(1505): Process: com.example.sqlitedemoo, PID: 1505
12-22 10:03:59.897: E/AndroidRuntime(1505): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.sqlitedemoo/com.pavan.sqlitedemoo.MainActivity}: java.lang.NullPointerException
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.os.Handler.dispatchMessage(Handler.java:102)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.os.Looper.loop(Looper.java:136)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.app.ActivityThread.main(ActivityThread.java:5017)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at java.lang.reflect.Method.invokeNative(Native Method)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at java.lang.reflect.Method.invoke(Method.java:515)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at dalvik.system.NativeStart.main(Native Method)
12-22 10:03:59.897: E/AndroidRuntime(1505): Caused by: java.lang.NullPointerException
12-22 10:03:59.897: E/AndroidRuntime(1505):     at com.pavan.sqlitedemoo.MainActivity.onCreate(MainActivity.java:50)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.app.Activity.performCreate(Activity.java:5231)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
12-22 10:03:59.897: E/AndroidRuntime(1505):     ... 11 more

public class MainActivity extends Activity {

    ListView lv;
    SQLController dbcon;
    TextView memID_tv, memName_tv;

    Button delete_btn;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        dbcon = new SQLController(this);
        dbcon.open();
        lv = (ListView) findViewById(R.id.memberList_id);
        delete_btn = (Button) findViewById(R.id.delete_btn);

        // Attach The Data From DataBase Into ListView Using Crusor Adapter
        Cursor cursor = dbcon.readData();
        String[] from = new String[] { DBhelper.MEMBER_ID, DBhelper.MEMBER_NAME };
        int[] to = new int[] { R.id.member_id, R.id.member_name };

        @SuppressWarnings("deprecation")
        SimpleCursorAdapter adapter = new SimpleCursorAdapter(
                MainActivity.this, R.layout.view_member_entry, cursor, from, to);

        adapter.notifyDataSetChanged();
        lv.setAdapter(adapter);


        delete_btn.setOnClickListener(new OnClickListener() { --> 50th Line- Null pointer Exception
            @Override
            public void onClick(View v) {

                memID_tv = (TextView) v.findViewById(R.id.member_id);
                memName_tv = (TextView) v.findViewById(R.id.member_name);

                String memberID_val = memID_tv.getText().toString();
                String memberName_val = memName_tv.getText().toString();

                Intent modify_intent = new Intent(getApplicationContext(),
                        Modify_member.class);
                modify_intent.putExtra("memberName", memberName_val);
                modify_intent.putExtra("memberID", memberID_val);
                startActivity(modify_intent);
            }
        });

    }

MainActivity.java:

12-22 10:03:59.897: E/AndroidRuntime(1505): FATAL EXCEPTION: main
12-22 10:03:59.897: E/AndroidRuntime(1505): Process: com.example.sqlitedemoo, PID: 1505
12-22 10:03:59.897: E/AndroidRuntime(1505): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.sqlitedemoo/com.pavan.sqlitedemoo.MainActivity}: java.lang.NullPointerException
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.os.Handler.dispatchMessage(Handler.java:102)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.os.Looper.loop(Looper.java:136)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.app.ActivityThread.main(ActivityThread.java:5017)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at java.lang.reflect.Method.invokeNative(Native Method)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at java.lang.reflect.Method.invoke(Method.java:515)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at dalvik.system.NativeStart.main(Native Method)
12-22 10:03:59.897: E/AndroidRuntime(1505): Caused by: java.lang.NullPointerException
12-22 10:03:59.897: E/AndroidRuntime(1505):     at com.pavan.sqlitedemoo.MainActivity.onCreate(MainActivity.java:50)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.app.Activity.performCreate(Activity.java:5231)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
12-22 10:03:59.897: E/AndroidRuntime(1505):     ... 11 more

public class MainActivity extends Activity {

    ListView lv;
    SQLController dbcon;
    TextView memID_tv, memName_tv;

    Button delete_btn;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        dbcon = new SQLController(this);
        dbcon.open();
        lv = (ListView) findViewById(R.id.memberList_id);
        delete_btn = (Button) findViewById(R.id.delete_btn);

        // Attach The Data From DataBase Into ListView Using Crusor Adapter
        Cursor cursor = dbcon.readData();
        String[] from = new String[] { DBhelper.MEMBER_ID, DBhelper.MEMBER_NAME };
        int[] to = new int[] { R.id.member_id, R.id.member_name };

        @SuppressWarnings("deprecation")
        SimpleCursorAdapter adapter = new SimpleCursorAdapter(
                MainActivity.this, R.layout.view_member_entry, cursor, from, to);

        adapter.notifyDataSetChanged();
        lv.setAdapter(adapter);


        delete_btn.setOnClickListener(new OnClickListener() { --> 50th Line- Null pointer Exception
            @Override
            public void onClick(View v) {

                memID_tv = (TextView) v.findViewById(R.id.member_id);
                memName_tv = (TextView) v.findViewById(R.id.member_name);

                String memberID_val = memID_tv.getText().toString();
                String memberName_val = memName_tv.getText().toString();

                Intent modify_intent = new Intent(getApplicationContext(),
                        Modify_member.class);
                modify_intent.putExtra("memberName", memberName_val);
                modify_intent.putExtra("memberID", memberID_val);
                startActivity(modify_intent);
            }
        });

    }

我需要什么：

12-22 10:03:59.897: E/AndroidRuntime(1505): FATAL EXCEPTION: main
12-22 10:03:59.897: E/AndroidRuntime(1505): Process: com.example.sqlitedemoo, PID: 1505
12-22 10:03:59.897: E/AndroidRuntime(1505): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.sqlitedemoo/com.pavan.sqlitedemoo.MainActivity}: java.lang.NullPointerException
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.os.Handler.dispatchMessage(Handler.java:102)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.os.Looper.loop(Looper.java:136)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.app.ActivityThread.main(ActivityThread.java:5017)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at java.lang.reflect.Method.invokeNative(Native Method)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at java.lang.reflect.Method.invoke(Method.java:515)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at dalvik.system.NativeStart.main(Native Method)
12-22 10:03:59.897: E/AndroidRuntime(1505): Caused by: java.lang.NullPointerException
12-22 10:03:59.897: E/AndroidRuntime(1505):     at com.pavan.sqlitedemoo.MainActivity.onCreate(MainActivity.java:50)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.app.Activity.performCreate(Activity.java:5231)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
12-22 10:03:59.897: E/AndroidRuntime(1505):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
12-22 10:03:59.897: E/AndroidRuntime(1505):     ... 11 more

public class MainActivity extends Activity {

    ListView lv;
    SQLController dbcon;
    TextView memID_tv, memName_tv;

    Button delete_btn;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        dbcon = new SQLController(this);
        dbcon.open();
        lv = (ListView) findViewById(R.id.memberList_id);
        delete_btn = (Button) findViewById(R.id.delete_btn);

        // Attach The Data From DataBase Into ListView Using Crusor Adapter
        Cursor cursor = dbcon.readData();
        String[] from = new String[] { DBhelper.MEMBER_ID, DBhelper.MEMBER_NAME };
        int[] to = new int[] { R.id.member_id, R.id.member_name };

        @SuppressWarnings("deprecation")
        SimpleCursorAdapter adapter = new SimpleCursorAdapter(
                MainActivity.this, R.layout.view_member_entry, cursor, from, to);

        adapter.notifyDataSetChanged();
        lv.setAdapter(adapter);


        delete_btn.setOnClickListener(new OnClickListener() { --> 50th Line- Null pointer Exception
            @Override
            public void onClick(View v) {

                memID_tv = (TextView) v.findViewById(R.id.member_id);
                memName_tv = (TextView) v.findViewById(R.id.member_name);

                String memberID_val = memID_tv.getText().toString();
                String memberName_val = memName_tv.getText().toString();

                Intent modify_intent = new Intent(getApplicationContext(),
                        Modify_member.class);
                modify_intent.putExtra("memberName", memberName_val);
                modify_intent.putExtra("memberID", memberID_val);
                startActivity(modify_intent);
            }
        });

    }

---

我在adaper xml（view\u member\u entry.xml）中添加了

Delete

按钮。因为我需要对每个列表视图行项目执行

delete

操作。任何人都可以帮助我。谢谢。

主活动的布局文件是activity\u main.xml:，并且它没有名为delete\u btn的元素作为按钮，但是有一个按钮作为查看成员条目的元素。xml:，

您正在活动中加载活动主项，并试图从中获取删除。但是在该布局xml中没有任何

delete\u btn

。检查你的代码。

@stealthjong

delete\u btn.setOnClickListener（新OnClickListener（）{-->Null指针异常

我已经提到过清理你的项目（project->Clean）你的delete\u btn不是你试图定位它的主布局的一部分（显然，它会抛出一个NPE）。它是在适配器中膨胀的布局的一部分，用作列表视图项（可以有多个）。使用自定义适配器并在其中定义删除逻辑（或使用接口在“活动”中执行此操作）。这里的一个例子：我已经知道了。请仔细阅读问题。我需要的是：

我在adaper xml中添加了删除按钮（view\u member\u entry.xml）。因为我需要对每个列表视图行项目执行删除操作。

对此有任何建议。您对布局的整个想法都乱七八糟。您无法从其他布局中获取按钮并尝试在其他位置使用它。如果要将onclick listener设置为使用view创建的按钮，我们会为您当前的问题编写答案_成员项布局，然后将onclick侦听器设置为按钮delete\u btn from the custome adapter！这不是将onclick侦听器添加到此按钮的方法因为listview需要一个custome布局，最好通过custome adapter。