更改圖像在按鈕點擊一個xml頁面。android

Question

我有一個2 spinners，根據那裏組合，按鈕上點擊打開一個新的xml，其中一個圖像將顯示基於來自spinners的組合。

基本上iam面臨2個問題。

1. 按鈕onClickListner（）不工作，以及我評論的功能和向前邁進

2. 的image.setImageResource（）不工作logcat的說，他是無法啓動的活動。

那我到底做錯了什麼？

這是主要的活動代碼..一切之前嘗試的作品完美..但的onclick聽者（）崩潰的代碼..但在徵求意見PRG工程..

try 
    { 
     /*btn=(Button)this.findViewById(R.id.button); 
     System.out.println(btn); 
     btn.setOnClickListener(new OnClickListener() {    

      public void onClick(View v) {*/ 

       if(subtxt.equals("Maths")) 
       { 
        if(Integer.parseInt(yeartxt)==1990) 
        { 
         Intent ip = new Intent(MainActivity.this, maths.class); 
         startActivity(ip); 
        } 
. 
//the prg executes until start activity perfectly and continues onto maths.class 
. 

. 

這是在代碼maths.java

protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
ImageView image; 
image = (ImageView) findViewById(R.id.imageView1); 
image.setImageResource(R.drawable.heart_maths); 
setContentView(R.layout.physics); 
    } 

所有的活動都在Android的mainfest指定.. 這是日誌貓

02-13 00:29:20.908: E/AndroidRuntime(1485): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245) 
02-13 00:29:20.908: E/AndroidRuntime(1485): at android.app.ActivityThread.access$800(ActivityThread.java:135) 
02-13 00:29:20.908: E/AndroidRuntime(1485): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196) 
02-13 00:29:20.908: E/AndroidRuntime(1485): at android.os.Handler.dispatchMessage(Handler.java:102) 
02-13 00:29:20.908: E/AndroidRuntime(1485): at android.os.Looper.loop(Looper.java:136) 
02-13 00:29:20.908: E/AndroidRuntime(1485): at android.app.ActivityThread.main(ActivityThread.java:5017) 
02-13 00:29:20.908: E/AndroidRuntime(1485): at java.lang.reflect.Method.invokeNative(Native Method) 
02-13 00:29:20.908: E/AndroidRuntime(1485): at java.lang.reflect.Method.invoke(Method.java:515) 
02-13 00:29:20.908: E/AndroidRuntime(1485): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) 
02-13 00:29:20.908: E/AndroidRuntime(1485): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) 
02-13 00:29:20.908: E/AndroidRuntime(1485): at dalvik.system.NativeStart.main(Native Method) 
02-13 00:29:20.908: E/AndroidRuntime(1485): Caused by: java.lang.NullPointerException 
02-13 00:29:20.908: E/AndroidRuntime(1485): at com.example.subjects.maths.onCreate(maths.java:16) 
02-13 00:29:20.908: E/AndroidRuntime(1485): at android.app.Activity.performCreate(Activity.java:5231) 
02-13 00:29:20.908: E/AndroidRuntime(1485): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087) 
02-13 00:29:20.908: E/AndroidRuntime(1485): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159) 
02-13 00:29:20.908: E/AndroidRuntime(1485): ... 11 more 

那麼究竟是在這裏面臨的2個錯誤的原因。 ??

編輯ANSWER

1) the on clicklistner() error can be avoided by declaring all variables globally in mainactivity.java 
2) the image.setImageResource() should be given after setcontentview.. 

這是所有有。

Answer 1

你去錯在這裏：第一setContentView(R.layout.physics)並得到後imageoncreate()方法：

您應該格式如下圖所示：

image = (ImageView) findViewById(R.id.imageView1); 
image.setImageResource(R.drawable.heart_maths); 
setContentView(R.layout.physics); 

與

setContentView(R.layout.physics); 
image = (ImageView) findViewById(R.id.imageView1); 
image.setImageResource(R.drawable.heart_maths); 

Answer 2

替換爲此，您需要先設置視圖然後使用資源。將行setContentView(R.layout.physics);移至頂部。

protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
setContentView(R.layout.physics); 
ImageView image; 
image = (ImageView) findViewById(R.id.imageView1); 
image.setImageResource(R.drawable.heart_maths); 

    } 

Answer 3

改變此密碼

protected void onCreate(Bundle savedInstanceState) { 
super.onCreate(savedInstanceState); 
ImageView image; 
image = (ImageView) findViewById(R.id.imageView1); 
image.setImageResource(R.drawable.heart_maths); 
setContentView(R.layout.physics); 
} 

到

protected void onCreate(Bundle savedInstanceState) { 
super.onCreate(savedInstanceState); 
setContentView(R.layout.physics); 
ImageView image; 
image = (ImageView) findViewById(R.id.imageView1); 
image.setImageResource(R.drawable.heart_maths); 

}