模擬器顯示「不幸的應用程序已停止」

Question

雖然我正在調試代碼，它顯示沒有錯誤...但在運行應用程序時，它顯示「不幸的應用程序已停止」。這是我的活動2頁...從這同時單擊下一步按鈕應該移動到活動3個page.this頁是我的活動第2頁

     package com.example.admin.androidapp; 

     import android.app.Activity; 
     import android.content.Context; 
     import android.content.Intent; 
     import android.os.Bundle; 
     import android.widget.Button; 
     import android.view.View; 
     import android.view.View.OnClickListener; 
     import android.widget.Toast; 

     public class Activity2 extends Activity { 

      Button btn11; 
      Button btn22; 
      public Intent intent; 
      Button btn; 



      @Override 
      public void onCreate(Bundle savedInstanceState) { 
       super.onCreate(savedInstanceState); 

       setContentView(R.layout.activity_activity2); 

       btn11 = (Button) findViewById(R.id.button2); 
       btn22 = (Button) findViewById(R.id.button5); 

       btn = (Button) findViewById(R.id.button2); 
       btn.setOnClickListener(new View.OnClickListener() { 
        @Override 
        public void onClick(View v) { 
         switch (v.getId()) { 
          case R.id.button2: 
           intent = new Intent(Activity2.this, Activity3.class); 
           startActivity(intent); 
           break; 

          case R.id.button5: 
           intent= new Intent(Activity2.this, Welcome.class); 
           startActivity(intent); 
           break; 


         } 
        } 

       }); 

      } 





     } 

=============================================================== 

here is my Activity3 page: 


    package com.example.admin.androidapp; 

import android.app.Activity; 
import android.content.Intent; 
import android.os.Bundle; 
import android.widget.Button; 
import android.widget.RadioButton; 
import android.widget.RadioGroup; 

    public class Activity3 extends Activity{ 
    RadioGroup radiogroup; 
    Button btn1; 
    private Intent mIntent; 

    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_activity3); 

     radiogroup = (RadioGroup) findViewById(R.id.radiogroup); 
     btn1 = (Button) findViewById(R.id.button); 

     radiogroup.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() { 



@Override 
     public void onCheckedChanged(RadioGroup radioGroup, int RadioID) { 
       RadioButton rd = (RadioButton) radioGroup.findViewById(RadioID); 


    switch (rd.getId()) { 
    case R.id.radioButton7: 
         mIntent = new Intent(Activity3.this, Terminate.class); 
         break; 
    case R.id.radioButton8: 
        mIntent = new Intent(Activity3.this, Activity4.class); 
        break; 
    case R.id.radioButton10: 
        mIntent = new Intent(Activity3.this, Activity4.class); 
        break; 
    case R.id.radioButton11: 
        mIntent = new Intent(Activity3.this, Activity4.class); 
        break; 
    case R.id.radioButton15: 
        mIntent = new Intent(Activity3.this, Activity4.class); 
        break; 
    case R.id.radioButton16: 
        mIntent = new Intent(Activity3.this, Activity4.class); 
        break; 
    case R.id.radioButton17: 
        mIntent = new Intent(Activity3.this, Activity4.class); 
        break; 
    case R.id.radioButton18: 
        mIntent = new Intent(Activity3.this, Activity4.class); 
        break; 
    case R.id.radioButton19: 
        mIntent = new Intent(Activity3.this, Activity4.class); 
        break; 
    case R.id.radioButton13: 
        mIntent = new Intent(Activity3.this, Activity4.class); 
        break; 
    case R.id.radioButton12: 
        mIntent = new Intent(Activity3.this, Activity4.class); 
        break; 
     case R.id.radioButton14: 
        mIntent = new Intent(Activity3.this, Activity4.class); 
        break; 
    } 
     } 
    } 

======================== ================== 請檢查上面的代碼，並幫助我在這個問題.. 在此先感謝。 和即時消息在logcat中，而單擊按鈕像java.lang.NullPointerException：試圖調用虛擬方法

Answer 1

問題是你打電話onclick爲oncreate以外的btn。在你的onCreate中移動下面的代碼。你也需要initialise按鈕

Button btn = (Button) findViewById(R.id.btn); 
btn.setOnClickListener(new View.OnClickListener() { 
        @Override 
        public void onClick(View view) { 
         if (intent != null) { 
          startActivity(intent); 
         } else { 
          Toast.makeText(getApplicationContext(), "No choice made yet", Toast.LENGTH_SHORT).show(); 
         } 


        } 

       }); 

編輯：

試試這個

btn.setOnClickListener(new View.OnClickListener() { 
         @Override 
         public void onClick(View view) { 
          Intent intent = new Intent(Activity2.this, Activity3.class); 
    startActivity(intent); 

         } 

        }); 

你不是已經初始化意圖所以它總是空，因此它進入其他條件。你在那裏添加吐司。

Toast.makeText(getApplicationContext(), "No choice made yet", Toast.LENGTH_SHORT).show(); 

這是顯示。