Android onClickListener NullPointerException

Question

所有.我搜索过,但找不到任何可以帮我解决这个问题的东西.

由于NullPointerException,我的应用程序几乎在启动时立即退出.我怀疑问题可能是我使用可绘制图像(ImageView)而不是按钮(视图)作为你点击的东西.

谢谢你的帮助.这让我疯狂了好几个小时!

代码如下:

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);
    }
}

和堆栈如下:

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]  

Answer 1

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

你不能R.drawable用来检索物品.你必须使用R.id

Answer 2

要获得View的Id,请使用R.id而不是R.drawable,更改

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

至

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

并设置drawable使用 blankTile.setImageResource(R.drawable.zero);