Question

这是我的问题。我创建了一个按钮ID：“fibo1”。此按钮属于“CList”活动。点击按钮后，我想打开另一个名为“斐波那契”的活动

'CList'的XML

 <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical" >

        <Button
            android:id="@+id/fibo1"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:onClick="sendMessage"
            android:text="Fibo" />

CList的Java

public class CList extends Activity {
    Button read1;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.list);


        read1 = (Button) findViewById (R.id.fibo1);
        read1.setOnClickListener (new OnClickListener(){
            @Override
            public void onClick (View v){
                Intent intent = new Intent (CList.this,Fibonacci.class);
                startActivity (intent);
                finish();
            }
       });
    }

应用程序在从主活动打开“列表”活动时崩溃。 Log Cat提供错误Fatal Exception :main。我已将这些活动添加到Android Manifest。我只是一个初学者，如果我的术语不正确，请原谅我。

这是Log Cat

03-07 19:33:29.931: E/AndroidRuntime(19565): FATAL EXCEPTION: main

03-07 19:33:29.931: E/AndroidRuntime(19565): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.geek.cprogramspopular/com.geek.cprogramspopular.CList}: java.lang.NullPointerException

03-07 19:33:29.931: E/AndroidRuntime(19565):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2245)

03-07 19:33:29.931: E/AndroidRuntime(19565):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2299)

03-07 19:33:29.931: E/AndroidRuntime(19565):    at android.app.ActivityThread.access$700(ActivityThread.java:150)

03-07 19:33:29.931: E/AndroidRuntime(19565):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1280)

03-07 19:33:29.931: E/AndroidRuntime(19565):    at android.os.Handler.dispatchMessage(Handler.java:99)

03-07 19:33:29.931: E/AndroidRuntime(19565):    at android.os.Looper.loop(Looper.java:137)

03-07 19:33:29.931: E/AndroidRuntime(19565):    at android.app.ActivityThread.main(ActivityThread.java:5283)

03-07 19:33:29.931: E/AndroidRuntime(19565):    at java.lang.reflect.Method.invokeNative(Native Method)

03-07 19:33:29.931: E/AndroidRuntime(19565):    at java.lang.reflect.Method.invoke(Method.java:511)

03-07 19:33:29.931: E/AndroidRuntime(19565):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102)

03-07 19:33:29.931: E/AndroidRuntime(19565):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869)

03-07 19:33:29.931: E/AndroidRuntime(19565):    at dalvik.system.NativeStart.main(Native Method)

03-07 19:33:29.931: E/AndroidRuntime(19565): Caused by: java.lang.NullPointerException

03-07 19:33:29.931: E/AndroidRuntime(19565):    at com.geek.cprogramspopular.CList.onCreate(CList.java:23)

03-07 19:33:29.931: E/AndroidRuntime(19565):    at android.app.Activity.performCreate(Activity.java:5283)

03-07 19:33:29.931: E/AndroidRuntime(19565):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1097)

03-07 19:33:29.931: E/AndroidRuntime(19565):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2209)

03-07 19:33:29.931: E/AndroidRuntime(19565):    ... 11 more

Answer 1

您只需从XML文件中删除此行，您无需在Intent Calling中完成您的活动......

android:onClick="sendMessage"
read1.setOnClickListener (new OnClickListener(){
        @Override
        public void onClick (View v){
            Intent intent = new Intent (CList.this,Fibonacci.class);
            startActivity (intent);                
        }
   });

Answer 2

使用以下代码 -

public void sendMessage(View v) {

     Intent intent = new Intent(CList.this, Fibonacci.class);
     startAcitivty(intent);
}

在onCreate(Bundle savedInstanceState)方法之后，而不是 -

read1.setOnClickListener (new OnClickListener(){
        @Override
        public void onClick (View v){
            Intent intent = new Intent (CList.this,Fibonacci.class);
            startActivity(intent);
            finish();
}

执行此操作后，您也可以删除Button read1;和read1 = (Button) findViewById (R.id.fibo1);。

单击Android应用程序中的按钮打开新活动

2 个答案: