我的安卓程序不工作了，因为它看不到按钮点击功能.有人能帮我吗?

Question

我不能运行我的Android程序，因为按钮点击功能。有人能帮我吗?

我有这样的代码:

public class MainActivity extends ActionBarActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button btn1 = (Button) findViewById(R.id.button1);
        btn1.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v)
            {
        }       
        }); 
        if (savedInstanceState == null) {
            getSupportFragmentManager().beginTransaction()
                    .add(R.id.container, new PlaceholderFragment()).commit();
        }
    }
}

当我注释掉Button代码时，一切正常

 public class MainActivity extends ActionBarActivity {
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            /*
            Button btn1 = (Button) findViewById(R.id.button1);
            btn1.setOnClickListener(new View.OnClickListener() {
                public void onClick(View v)
                {
            }       
            }); */
            if (savedInstanceState == null) {
                getSupportFragmentManager().beginTransaction()
                        .add(R.id.container, new PlaceholderFragment()).commit();
            }
        }
    }

如果不在解说词程序中未执行。

错误信息:不幸的是，"programname"已停止。

logcat错误:

06-06 06:21:11.950: E/AndroidRuntime(1866):     at android.os.Looper.loop(Looper.java:136)
06-06 08:37:02.183: E/AndroidRuntime(2380): FATAL EXCEPTION: main
06-06 08:37:02.183: E/AndroidRuntime(2380): Process: com.example.searchpersons, PID: 2380
06-06 08:37:02.183: E/AndroidRuntime(2380): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.searchpersons/com.example.searchpersons.MainActivity}: java.lang.NullPointerException
06-06 08:37:02.183: E/AndroidRuntime(2380):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
06-06 08:37:02.183: E/AndroidRuntime(2380):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
06-06 08:37:02.183: E/AndroidRuntime(2380):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
06-06 08:37:02.183: E/AndroidRuntime(2380):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
06-06 08:37:02.183: E/AndroidRuntime(2380):     at android.os.Handler.dispatchMessage(Handler.java:102)
06-06 08:37:02.183: E/AndroidRuntime(2380):     at android.os.Looper.loop(Looper.java:136)
06-06 08:37:02.183: E/AndroidRuntime(2380):     at android.app.ActivityThread.main(ActivityThread.java:5017)
06-06 08:37:02.183: E/AndroidRuntime(2380):     at java.lang.reflect.Method.invokeNative(Native Method)
06-06 08:37:02.183: E/AndroidRuntime(2380):     at java.lang.reflect.Method.invoke(Method.java:515)
06-06 08:37:02.183: E/AndroidRuntime(2380):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
06-06 08:37:02.183: E/AndroidRuntime(2380):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
06-06 08:37:02.183: E/AndroidRuntime(2380):     at dalvik.system.NativeStart.main(Native Method)
06-06 08:37:02.183: E/AndroidRuntime(2380): Caused by: java.lang.NullPointerException
06-06 08:37:02.183: E/AndroidRuntime(2380):     at com.example.searchpersons.MainActivity.onCreate(MainActivity.java:41)
06-06 08:37:02.183: E/AndroidRuntime(2380):     at android.app.Activity.performCreate(Activity.java:5231)
06-06 08:37:02.183: E/AndroidRuntime(2380):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
06-06 08:37:02.183: E/AndroidRuntime(2380):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
06-06 08:37:02.183: E/AndroidRuntime(2380):     ... 11 more

我修复它^_^。我将代码插入到这个函数中:

 public static class PlaceholderFragment extends Fragment { 
          public PlaceholderFragment() { } 
          @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
                 final View rootView = inflater.inflate(R.layout.fragment_main, container, false);          
                 Button btn1 = (Button) rootView.findViewById(R.id.button1);          
                 btn1.setOnClickListener(new View.OnClickListener() 
                 { 
                        public void onClick(View v) 
                        { }    
                 }       
                 return rootView;
           }
    } 

一切正常:)))

Answer 1

打开activity_main.xml布局文件，您将其设置为setContentView(R.layout.activity_main)中的布局。确保布局文件中有一个button1，例如:

<Button
  android:layout_height="wrap_content"
  android:layout_width="wrap_content"
  android:id="@+id/button1"
  android:text="Button"
/>

发生的是，findViewById(R.id.button1)不能找到视图在您的布局。所以，确保它在那里。如果你能发布你的activity_main.xml文件，这将有助于我们解决问题。