如果導致程序強制關閉的條件

Question

我正在做一個android應用程序，我正在考慮創建一個主題選項。那麼我想要做的就是讓用戶點擊代表主題的圖像按鈕。當他點擊它時，我開始一個新的活動，即我將他引導到主頁。另外我創建了幾個整數變量，當用戶點擊一個按鈕時，它們被設置爲1。

然後在其他類中，我所做的只是檢查變量是否爲1，並取決於我應用的主題。按主題我的意思是我只是改變背景壁紙。但是這不起作用。我的意思是代碼有效，但如果使用if循環來檢查變量值，然後應用效果，則會導致錯誤。

下面是完整的代碼：

package com.example.themetest; 

import android.os.Bundle; 
import android.app.Activity; 
import android.content.Intent; 
import android.view.Menu; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.widget.ImageButton; 
import android.widget.LinearLayout; 

public class MainActivity extends Activity implements OnClickListener{ 

    ImageButton ib1; 
    ImageButton ib2; 
    int water=0; 
    int fire=0; 


    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 

     ib1 = (ImageButton) findViewById(R.id.imageButton1); 
     ib2 = (ImageButton) findViewById(R.id.imageButton2); 
     ib1.setOnClickListener(this); 
     ib2.setOnClickListener(this); 



    } 


    @Override 
    public void onClick(View v) { 
     // TODO Auto-generated method stub 

     switch(v.getId()){ 
     case R.id.imageButton1: 
      water = 1; 
      Intent wi = new Intent("com.example.themetest.THEME"); 
      startActivity(wi); 
      break; 

     case R.id.imageButton2: 
      fire = 1; 
      Intent fi = new Intent("com.example.themetest.THEME"); 
      startActivity(fi); 
      break; 
     } 
    } 



} 

下面是其他類，其中i檢查哪些變量設置爲1和應用效果。

package com.example.themetest; 

import java.io.InputStream; 

import android.app.Activity; 
import android.content.res.Resources; 
import android.graphics.Bitmap; 
import android.graphics.BitmapFactory; 
import android.graphics.drawable.Drawable; 
import android.os.Bundle; 
import android.widget.EditText; 
import android.widget.LinearLayout; 

public class Theme extends Activity{ 

    MainActivity main; 
    Resources res; 
    Drawable drawable; 
    LinearLayout linearLayout; 




    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.theme); 

     if(main.water==1){ 


      res = getResources(); 
      drawable = res.getDrawable(R.drawable.water_theme); 
      linearLayout = (LinearLayout)findViewById(R.id.ll); 
      linearLayout.setBackgroundDrawable(drawable); 
      } 
      else if(main.fire==1){ 
       res = getResources(); 
       drawable = res.getDrawable(R.drawable.fire_theme); 
       linearLayout = (LinearLayout)findViewById(R.id.ll); 
       linearLayout.setBackgroundDrawable(drawable); 
     } 
      else{ 
       res = getResources(); 
       drawable = res.getDrawable(R.drawable.ic_launcher); 
       linearLayout = (LinearLayout)findViewById(R.id.ll); 
       linearLayout.setBackgroundDrawable(drawable); 
     } 

    } 



    } 

我可以改變牆紙，而不使用if循環，但我想這樣來做這是行不通的。任何人都可以告訴我爲什麼？

登錄貓：

01-15 12:08:23.339: D/dalvikvm(273): GC_EXTERNAL_ALLOC freed 767 objects/55936 bytes in 235ms 
01-15 12:08:25.539: D/AndroidRuntime(273): Shutting down VM 
01-15 12:08:25.539: W/dalvikvm(273): threadid=1: thread exiting with uncaught exception (group=0x4001d800) 
01-15 12:08:25.559: E/AndroidRuntime(273): FATAL EXCEPTION: main 
01-15 12:08:25.559: E/AndroidRuntime(273): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.themetest/com.example.themetest.Theme}: java.lang.NullPointerException 
01-15 12:08:25.559: E/AndroidRuntime(273): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663) 
01-15 12:08:25.559: E/AndroidRuntime(273): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679) 
01-15 12:08:25.559: E/AndroidRuntime(273): at android.app.ActivityThread.access$2300(ActivityThread.java:125) 
01-15 12:08:25.559: E/AndroidRuntime(273): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033) 
01-15 12:08:25.559: E/AndroidRuntime(273): at android.os.Handler.dispatchMessage(Handler.java:99) 
01-15 12:08:25.559: E/AndroidRuntime(273): at android.os.Looper.loop(Looper.java:123) 
01-15 12:08:25.559: E/AndroidRuntime(273): at android.app.ActivityThread.main(ActivityThread.java:4627) 
01-15 12:08:25.559: E/AndroidRuntime(273): at java.lang.reflect.Method.invokeNative(Native Method) 
01-15 12:08:25.559: E/AndroidRuntime(273): at java.lang.reflect.Method.invoke(Method.java:521) 
01-15 12:08:25.559: E/AndroidRuntime(273): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) 
01-15 12:08:25.559: E/AndroidRuntime(273): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626) 
01-15 12:08:25.559: E/AndroidRuntime(273): at dalvik.system.NativeStart.main(Native Method) 
01-15 12:08:25.559: E/AndroidRuntime(273): Caused by: java.lang.NullPointerException 
01-15 12:08:25.559: E/AndroidRuntime(273): at com.example.themetest.Theme.onCreate(Theme.java:29) 
01-15 12:08:25.559: E/AndroidRuntime(273): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
01-15 12:08:25.559: E/AndroidRuntime(273): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627) 
01-15 12:08:25.559: E/AndroidRuntime(273): ... 11 more 
01-15 12:08:31.089: I/Process(273): Sending signal. PID: 273 SIG: 9 

Answer 1

您不能訪問其他活動的變量這種方式，更好的方法（例如）是使用恆定類..

public class Constants { 
    public static int water=0; 
    public staticint fire=0; 
} 

MainActivity：

@Override 
public void onClick(View v) { 
    // TODO Auto-generated method stub 

    switch(v.getId()){ 
    case R.id.imageButton1: 
     Constants.water = 1; 
     Intent wi = new Intent("com.example.themetest.THEME"); 
     startActivity(wi); 
     break; 

    case R.id.imageButton2: 
     Constants.fire = 1; 
     Intent fi = new Intent("com.example.themetest.THEME"); 
     startActivity(fi); 
     break; 
    } 
} 

主題：

protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.theme); 

    if(Constants.water==1){ 


     res = getResources(); 
     drawable = res.getDrawable(R.drawable.water_theme); 
     linearLayout = (LinearLayout)findViewById(R.id.ll); 
     linearLayout.setBackgroundDrawable(drawable); 
     } 
     else if(Constants.fire==1){ 
      res = getResources(); 
      drawable = res.getDrawable(R.drawable.fire_theme); 
      linearLayout = (LinearLayout)findViewById(R.id.ll); 
      linearLayout.setBackgroundDrawable(drawable); 
    } 
     else{ 
      res = getResources(); 
      drawable = res.getDrawable(R.drawable.ic_launcher); 
      linearLayout = (LinearLayout)findViewById(R.id.ll); 
      linearLayout.setBackgroundDrawable(drawable); 
    } 

} 

Answer 2

我認爲更好的方式來做到這一點是通過與意圖一起選擇的主題用戶的名稱或代碼。

這可能幫助：Passing data through Intent and receiving it