Android的onClickListener NullPointerException异常 [英] Android onClickListener NullPointerException

问题描述

所有。我已经搜查，但找不到任何可以帮助我解决这个问题。

我的应用程序几乎立即启动退出由于NullPointerException异常。我怀疑也许问题在于我使用一个绘制的图像（ImageView的），而不是为你的东西点击一个按钮（查看）。

感谢您的帮助。这已经快把我逼疯了好几个小时！

code是如下：

 包com.example.imageswitchermk2;进口android.app.Activity;
进口android.os.Bundle;
进口android.view.View;
进口android.view.View.OnClickListener;
进口android.view.Window;
进口android.widget.ImageView;公共类MainActivity扩展活动实现OnClickListener {
ImageView的blankTile;@覆盖
保护无效的onCreate（捆绑savedInstanceState）{
    super.onCreate（savedInstanceState）;
// requestWindowFeature（Window.FEATURE_NO_TITLE）;
    的setContentView（R.layout.activity_main）;
    blankTile =（ImageView的）findViewById（R.drawable.blank）;
    blankTile.setOnClickListener（本）; // 19行
}
    公共无效的onClick（视图v）{
        blankTile.setId（R.drawable.zero）;
    }
}
 

和堆栈如下：

 发[＆LT; 1 GT;主]（吊（例外的NullPointerException））
＆LT; VM不提供监控信息＆gt;
MainActivity.onCreate（捆绑）行：19
MainActivity（活动）.performCreate（包）行：5231
Instrumentation.callActivityOnCreate（活动，捆绑）行：1087
ActivityThread.performLaunchActivity（ActivityThread $ ActivityClientRecord，意图）行：2148
ActivityThread.handleLaunchActivity（ActivityThread $ ActivityClientRecord，意图）行：2233
ActivityThread.access $ 800（ActivityThread，ActivityThread $ ActivityClientRecord，意图）线：135
ActivityThread $ H.handleMessage（消息）行：1196
ActivityThread $ H（处理器）.dispatchMessage（消息）线：102
Looper.loop（）行：136
ActivityThread.main（字符串[]）行：5001
Method.invokeNative（对象，对象[]，上课，下课[]，类，整型，布尔）行：不可用[本机方法]
Method.invoke（对象，对象...）线：515
ZygoteInit $ MethodAndArgsCaller.run（）行：785
ZygoteInit.main（字符串[]）线：601
NativeStart.main（字符串[]）行：不可用[本机方法]
 

解决方案

  blankTile =（ImageView的）findViewById（R.drawable.blank）;
 

您不能使用 R.drawable 来检索项目。你必须使用 R.id

all. I've searched, but can't find anything that helps me fix this problem.

My app quits almost immediately on launch due to a NullPointerException. I suspect maybe the problem is that I'm using a drawable image (ImageView) rather than a button (View) as the thing you click on.

Thanks for any help. This has been driving me bonkers for hours!

Code is as follows:

package com.example.imageswitchermk2;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.Window;
import android.widget.ImageView;

public class MainActivity extends Activity implements OnClickListener{
ImageView blankTile;    

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
//        requestWindowFeature(Window.FEATURE_NO_TITLE);
    setContentView(R.layout.activity_main);
    blankTile = (ImageView) findViewById(R.drawable.blank); 
    blankTile.setOnClickListener(this); //LINE 19
}
    public void onClick(View v) {
        blankTile.setId(R.drawable.zero);
    }
}

and stack is as follows:

Thread [<1> main] (Suspended (exception NullPointerException))  
<VM does not provide monitor information>   
MainActivity.onCreate(Bundle) line: 19  
MainActivity(Activity).performCreate(Bundle) line: 5231 
Instrumentation.callActivityOnCreate(Activity, Bundle) line: 1087   
ActivityThread.performLaunchActivity(ActivityThread$ActivityClientRecord, Intent) line: 2148    
ActivityThread.handleLaunchActivity(ActivityThread$ActivityClientRecord, Intent) line: 2233 
ActivityThread.access$800(ActivityThread, ActivityThread$ActivityClientRecord, Intent) line: 135    
ActivityThread$H.handleMessage(Message) line: 1196  
ActivityThread$H(Handler).dispatchMessage(Message) line: 102    
Looper.loop() line: 136 
ActivityThread.main(String[]) line: 5001    
Method.invokeNative(Object, Object[], Class, Class[], Class, int, boolean) line: not available [native method]  
Method.invoke(Object, Object...) line: 515  
ZygoteInit$MethodAndArgsCaller.run() line: 785  
ZygoteInit.main(String[]) line: 601 
NativeStart.main(String[]) line: not available [native method]  

解决方案

blankTile = (ImageView) findViewById(R.drawable.blank); 

you can not use R.drawable to retrieve items. You have to use R.id

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