Question

主要活动

    @Override
            protected void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                setContentView(R.layout.welcome_page);
                login=(Button) findViewById(R.id.bLogin);
                register=(Button) findViewById(R.id.bRegister);
                login.setOnClickListener(new OnClickListener() {

                    @Override
                    public void onClick(View arg0) {
                        // TODO Auto-generated method stub
                        Intent intent1 = new Intent(arg0.getContext(),Sign_In.class);
                        startActivity(intent1);
                    }
                });
                register.setOnClickListener(new OnClickListener() {

                    @Override
                    public void onClick(View arg0) {
                        // TODO Auto-generated method stub
                        Intent intent2 = new Intent(arg0.getContext(),Register.class);
                        startActivity(intent2);

                    }
                });
            }


In Sign_In Activity:   

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.sign_in);
            Button blogin=(Button) findViewById(R.id.bLogin);
            blogin.setOnClickListener(new OnClickListener() {

                @Override
                public void onClick(View arg0) {
                    // TODO Auto-generated method stub
                    Intent intent = new Intent(arg0.getContext(),MessegeBox.class);
                    startActivity(intent);
                }
            });
        }

XML布局

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#FFFFFF"
    android:layout_gravity="center"
    android:orientation="vertical" >

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="top"
        android:layout_marginLeft="30dip"
        android:layout_marginRight="30dip"
        android:layout_marginTop="50dip"
        android:background="#FFFFFF"
        android:orientation="vertical" >

        <EditText
            android:id="@+id/phone_number"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="3dip"
            android:gravity="center"
            android:hint="Mobile Number"
            android:inputType="phone"
            android:maxLength="10" >

            <requestFocus />
        </EditText>

        <EditText
            android:id="@+id/phone_number"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="3dip"
            android:gravity="center"
            android:hint="Invivation Pin (If Any)"
            android:inputType="phone"
            android:maxLength="10" />

        <Button
            android:id="@+id/button1"
            style="@style/ButtonText"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="3dip"
            android:background="@drawable/blue_button"
            android:text="LOGIN" />
    </LinearLayout>

</LinearLayout>

这是log cat

01-10 00:40:49.897: E/AndroidRuntime(1030): FATAL EXCEPTION: main
01-10 00:40:49.897: E/AndroidRuntime(1030): java.lang.RuntimeException: Unable to start activity ComponentInfo{net.multiplesystem.nosms/net.multiplesystem.nosms.Sign_In}: java.lang.NullPointerException
01-10 00:40:49.897: E/AndroidRuntime(1030):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
01-10 00:40:49.897: E/AndroidRuntime(1030):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
01-10 00:40:49.897: E/AndroidRuntime(1030):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
01-10 00:40:49.897: E/AndroidRuntime(1030):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
01-10 00:40:49.897: E/AndroidRuntime(1030):     at android.os.Handler.dispatchMessage(Handler.java:99)
01-10 00:40:49.897: E/AndroidRuntime(1030):     at android.os.Looper.loop(Looper.java:137)
01-10 00:40:49.897: E/AndroidRuntime(1030):     at android.app.ActivityThread.main(ActivityThread.java:5103)
01-10 00:40:49.897: E/AndroidRuntime(1030):     at java.lang.reflect.Method.invokeNative(Native Method)
01-10 00:40:49.897: E/AndroidRuntime(1030):     at java.lang.reflect.Method.invoke(Method.java:525)
01-10 00:40:49.897: E/AndroidRuntime(1030):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
01-10 00:40:49.897: E/AndroidRuntime(1030):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
01-10 00:40:49.897: E/AndroidRuntime(1030):     at dalvik.system.NativeStart.main(Native Method)
01-10 00:40:49.897: E/AndroidRuntime(1030): Caused by: java.lang.NullPointerException
01-10 00:40:49.897: E/AndroidRuntime(1030):     at net.multiplesystem.nosms.Sign_In.onCreate(Sign_In.java:18)
01-10 00:40:49.897: E/AndroidRuntime(1030):     at android.app.Activity.performCreate(Activity.java:5133)
01-10 00:40:49.897: E/AndroidRuntime(1030):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
01-10 00:40:49.897: E/AndroidRuntime(1030):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
01-10 00:40:49.897: E/AndroidRuntime(1030):     ... 11 more

当我点击主要活动的登录按钮时。它显示空指针异常。已经尝试了很多，但无法解决问题。请告诉我我错在哪里。提前完成。

Answer 1

Button blogin=(Button) findViewById(R.id.bRegister);

我猜你引用了错误的id按钮。

您需要在sign_in.xml中检查按钮的ID。确保sign_in.xml中有按钮，并确保在java代码中引用时id匹配

我想它应该是R.id.bLogin

编辑：

你拥有的是

    <Button
        android:id="@+id/button1"

所以改变

 Button blogin=(Button) findViewById(R.id.bRegister);

到

Button bLogin = (Button)findViewById(R.id.button1);

此外，您已嵌套LinearLayout，但没有错，您可以拥有一个LinearLayout

Answer 2

试试这个..

更改

Button blogin=(Button) findViewById(R.id.blogin);

到

Button blogin=(Button) findViewById(R.id.button1);
            blogin.setOnClickListener(new OnClickListener() {

                @Override
                public void onClick(View arg0) {
                    // TODO Auto-generated method stub
                    Intent intent = new Intent(Sign_In.this,MessegeBox.class);
                    startActivity(intent);
                }
            });

Answer 3

Intent intent1 = new Intent(getApplicationContext(),Sign_In.class);
                    startActivity(intent1);

java.lang.RuntimeException：无法启动活动，java.lang.NullPointerException

3 个答案: