空指针异常

Question

我正在Eclipse Juno上创建一个移动应用程序，不同类的代码中没有错误，它将在模拟器上运行。但是，当第一个屏幕加载到模拟器上并且我选择其中一个按钮时，应用程序停止运行，并且我在日志cat中收到有关NullPointerException的错误，但似乎无法找到此问题的位置。有没有人有任何想法我做错了什么或导致应用程序停止的原因？

第一个屏幕上按钮的目的是将用户带到应用程序的不同区域，这样无需选择要去的区域，我就无法使用该应用程序。

这是我的第一个屏幕的代码：     package com.example.independentretailers;     import com.example.independentretailers.R;     import android.support.v7.app.ActionBarActivity;     import android.app.Activity;     import android.os.Bundle;     import android.view.Menu;     import android.view.MenuItem;     import android.view.View;     import android.view.View.OnClickListener;     import android.widget.Button;     import android.content。*;

public class welcome extends Activity {


public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.welcome);
addListenerOnButton();
addListenerOnButton1();
}

//to continue from welcome screen to customer login screen 
//when customer button is clicked 
public void addListenerOnButton() { 
Button CustomerButton = (Button) findViewById(R.id.button1);

CustomerButton.setOnClickListener(new OnClickListener(){

        @Override
        public void onClick(View v){
        Intent intent = new Intent   (getApplicationContext(),customerlogin.class);       
            startActivity(intent);

        }
    });
}

//to continue from welcome screen to retailer login screen 
//when retailer button is clicked 
public void addListenerOnButton1() { 
    Button RetailerButton = (Button) findViewById(R.id.button2);

    RetailerButton.setOnClickListener(new OnClickListener(){    

        @Override
        public void onClick(View v){
            Intent intent = new Intent (getApplicationContext(),retailerlogin.class);       
            startActivity(intent);

        }
    });

}
}

我的Log Cat错误是：

03-30 18:56:19.716: E/ResourceType(536): Style contains key with bad entry: 0x01010479
03-30 18:56:19.806: I/dalvikvm(536): threadid=3: reacting to signal 3
03-30 18:56:19.876: I/dalvikvm(536): Wrote stack traces to '/data/anr/traces.txt'
03-30 18:56:19.996: D/gralloc_goldfish(536): Emulator without GPU emulation detected.
03-30 18:58:31.936: E/ResourceType(536): Style contains key with bad entry: 0x01010479
03-30 18:58:31.966: D/AndroidRuntime(536): Shutting down VM
03-30 18:58:31.966: W/dalvikvm(536): threadid=1: thread exiting with uncaught exception (group=0x409c01f8)
03-30 18:58:32.016: E/AndroidRuntime(536): FATAL EXCEPTION: main
03-30 18:58:32.016: E/AndroidRuntime(536): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.independentretailers/com.example.independentretailers.customerlogin}: java.lang.NullPointerException
03-30 18:58:32.016: E/AndroidRuntime(536):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
03-30 18:58:32.016: E/AndroidRuntime(536):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
03-30 18:58:32.016: E/AndroidRuntime(536):  at android.app.ActivityThread.access$600(ActivityThread.java:123)
03-30 18:58:32.016: E/AndroidRuntime(536):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
03-30 18:58:32.016: E/AndroidRuntime(536):  at android.os.Handler.dispatchMessage(Handler.java:99)
03-30 18:58:32.016: E/AndroidRuntime(536):  at android.os.Looper.loop(Looper.java:137)
03-30 18:58:32.016: E/AndroidRuntime(536):  at android.app.ActivityThread.main(ActivityThread.java:4424)
03-30 18:58:32.016: E/AndroidRuntime(536):  at java.lang.reflect.Method.invokeNative(Native Method)
03-30 18:58:32.016: E/AndroidRuntime(536):  at java.lang.reflect.Method.invoke(Method.java:511)
03-30 18:58:32.016: E/AndroidRuntime(536):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
03-30 18:58:32.016: E/AndroidRuntime(536):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
03-30 18:58:32.016: E/AndroidRuntime(536):  at dalvik.system.NativeStart.main(Native Method)
03-30 18:58:32.016: E/AndroidRuntime(536): Caused by: java.lang.NullPointerException
03-30 18:58:32.016: E/AndroidRuntime(536):  at android.view.ViewGroup.addViewInner(ViewGroup.java:3336)
03-30 18:58:32.016: E/AndroidRuntime(536):  at android.view.ViewGroup.addView(ViewGroup.java:3208)
03-30 18:58:32.016: E/AndroidRuntime(536):  at android.view.ViewGroup.addView(ViewGroup.java:3188)
03-30 18:58:32.016: E/AndroidRuntime(536):  at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:270)
03-30 18:58:32.016: E/AndroidRuntime(536):  at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:260)
03-30 18:58:32.016: E/AndroidRuntime(536):  at android.app.Activity.setContentView(Activity.java:1855)
03-30 18:58:32.016: E/AndroidRuntime(536):  at com.example.independentretailers.customerlogin.onCreate(customerlogin.java:28)
03-30 18:58:32.016: E/AndroidRuntime(536):  at android.app.Activity.performCreate(Activity.java:4465)
03-30 18:58:32.016: E/AndroidRuntime(536):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
03-30 18:58:32.016: E/AndroidRuntime(536):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
03-30 18:58:32.016: E/AndroidRuntime(536):  ... 11 more
03-30 18:58:32.405: I/dalvikvm(536): threadid=3: reacting to signal 3
03-30 18:58:32.445: I/dalvikvm(536): Wrote stack traces to '/data/anr/traces.txt'
03-30 18:58:32.625: I/dalvikvm(536): threadid=3: reacting to signal 3
03-30 18:58:32.655: I/dalvikvm(536): Wrote stack traces to '/data/anr/traces.txt'

任何帮助都将非常感谢。

Answer 1

我认为你不必将一个按钮点击监听器嵌入到另一个按钮的onClickListener中。您还将按钮声明为实例变量并且没有初始化它们，然后在方法中声明了具有相同名称的本地按钮。删除它们中的任何一个以使它们工作。请尝试以下代码。

public class welcome extends Activity {
    //Button CustomerButton; No need to declare these here.
    //Button RetailerButton;

    public void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        setContentView(R.layout.welcome);
        addListenerOnButton();
        addListenerOnButton1();
    }

    //to continue from welcome screen to customer login screen 
    //when customer button is clicked 
    public void addListenerOnButton() { 
        Button CustomerButton = (Button) findViewById(R.id.button1);

        CustomerButton.setOnClickListener(new OnClickListener(){

            @Override
            public void onClick(View v){
                Intent intent = new Intent (getApplicationContext(),customerlogin.class);       
                startActivity(intent);

            }
        });
    }

    //to continue from welcome screen to retailer login screen 
    //when retailer button is clicked 
    public void addListenerOnButton1() { //This method was inside the first method earlier.
        Button RetailerButton = (Button) findViewById(R.id.button2);

        RetailerButton.setOnClickListener(new OnClickListener(){    

            @Override
            public void onClick(View v){
                Intent intent = new Intent (getApplicationContext(),retailerlogin.class);       
                startActivity(intent);

            }
        });

    }
}