無法啓動活動，setOnClickListener

Question

無法啓動新活動。在onClickListener中遇到問題。

我發表了一條錯誤代碼。不知道爲什麼我在這一行中出現錯誤。

我認爲它可以不初始化變量按鈕b，但它已初始化！

幫助，PLZ。

代碼：

public class newItem extends Activity { 
    private EditText Quantity; 
    private EditText Weight; 
    private EditText Price; 
    private EditText Title; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.new_list); 
     this.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, 
       WindowManager.LayoutParams.FLAG_FULLSCREEN); 

     Button b = (Button) findViewById(R.id.ok_but); 
     Quantity = (EditText) findViewById(R.id.Quantity); 
     Weight = (EditText) findViewById(R.id.Weight); 
     Price = (EditText) findViewById(R.id.Price); 
     Title = (EditText) findViewById(R.id.Title); 

     b.setOnClickListener(new OnClickListener() { 
      @Override 
      public void onClick(View v) { 
       Intent i = new Intent(); 
       i.putExtra("Quantity", Quantity.getText().toString()); 
       i.putExtra("Weight", Weight.getText().toString()); 
       i.putExtra("Price", Price.getText().toString()); 
       i.putExtra("Title", Title.getText().toString()); 
       setResult(RESULT_OK, i); 
       Log.i("palval", "setResult(RESULT_OK, i); newItem"); 
       finish(); 
      } 
     }); 
    } 
} 

錯誤：

07-08 17:26:42.402: E/AndroidRuntime(31626): FATAL EXCEPTION: main 
07-08 17:26:42.402: E/AndroidRuntime(31626): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.ashopping_list/com.example.ashopping_list.newItem}: java.lang.NullPointerException 
07-08 17:26:42.402: E/AndroidRuntime(31626): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2194) 
07-08 17:26:42.402: E/AndroidRuntime(31626): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2229) 
07-08 17:26:42.402: E/AndroidRuntime(31626): at android.app.ActivityThread.access$600(ActivityThread.java:139) 
07-08 17:26:42.402: E/AndroidRuntime(31626): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1261) 
07-08 17:26:42.402: E/AndroidRuntime(31626): at android.os.Handler.dispatchMessage(Handler.java:99) 
07-08 17:26:42.402: E/AndroidRuntime(31626): at android.os.Looper.loop(Looper.java:154) 
07-08 17:26:42.402: E/AndroidRuntime(31626): at android.app.ActivityThread.main(ActivityThread.java:4945) 
07-08 17:26:42.402: E/AndroidRuntime(31626): at java.lang.reflect.Method.invokeNative(Native Method) 
07-08 17:26:42.402: E/AndroidRuntime(31626): at java.lang.reflect.Method.invoke(Method.java:511) 
07-08 17:26:42.402: E/AndroidRuntime(31626): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 
07-08 17:26:42.402: E/AndroidRuntime(31626): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) 
07-08 17:26:42.402: E/AndroidRuntime(31626): at dalvik.system.NativeStart.main(Native Method) 
07-08 17:26:42.402: E/AndroidRuntime(31626): Caused by: java.lang.NullPointerException 
07-08 17:26:42.402: E/AndroidRuntime(31626): at com.example.ashopping_list.newItem.onCreate(newItem.java:32) 
07-08 17:26:42.402: E/AndroidRuntime(31626): at android.app.Activity.performCreate(Activity.java:4531) 
07-08 17:26:42.402: E/AndroidRuntime(31626): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1071) 
07-08 17:26:42.402: E/AndroidRuntime(31626): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2150) 

清單：

<activity 
     android:name=".newItem" 
     android:label="@string/title_activity_main" 
     android:windowSoftInputMode="stateAlwaysVisible" > 
    </activity> 

錯誤的位置：

b.setOnClickListener(new OnClickListener() { 

Answer 1

嘗試使用

implements View.OnClickListener 

或嘗試使用Listener作爲匿名類，然後告訴我它是否有效。

注：類名應該開始大寫，你應該尊重它。

更新：

所以問題是在其他地方，請確保您的ID是正確的！屬於Button。

Answer 2

你可以嘗試這樣的：

 Button b= (Button) findViewById(R.id.but_Ok); 
    b.setOnClickListener(new OnClickListener() { 
     public void onClick(View v) 
      { 
        Intent i = new Intent(FromYourActivity.this,NextActivity.class); 
        startActivity(i); 
        finish(); 
        ... 
      } 
     }); 

另外，還要確保你有正確的Button定義XML文件

 <Button 
    android:layout_height="wrap_content" 
    android:id="@+id/but_Ok" 
    android:text="Your Button Text" 
    android:layout_width="fill_parent" 
    /> 

Answer 3

您需要設置按鈕變量的onCreate以上（包）我也改變了onclick活動的設置方式試試這個

public class newItem extends Activity { 

private EditText Quantity; 
Button b; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.new_list); 
    Button b = (Button) findViewById(R.id.but_Ok); 
    b.setOnClickListener(new View.OnClickListener() { 

    public void onClick(View v) { 
    // TODO Auto-generated method stub 
    Intent i = new Intent(); 
    ... 
    setResult(RESULT_OK, i); 
    finish(); 
    } 
}); 


    } 
}