如果导致程序强制关闭的条件
问题描述：
我正在做一个android应用程序，我正在考虑创建一个主题选项。那么我想要做的就是让用户点击代表主题的图像按钮。当他点击它时，我开始一个新的活动，即我将他引导到主页。另外我创建了几个整数变量，当用户点击一个按钮时，它们被设置为1。如果导致程序强制关闭的条件
然后在其他类中，我所做的只是检查变量是否为1，并取决于我应用的主题。按主题我的意思是我只是改变背景壁纸。但是这不起作用。我的意思是代码有效，但如果使用if循环来检查变量值，然后应用效果，则会导致错误。
下面是完整的代码：
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;
}
}
}
下面是其他类，其中i检查哪些变量设置为1和应用效果。
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);
}
}
}
我可以改变墙纸，而不使用if循环，但我想这样来做这是行不通的。任何人都可以告诉我为什么？
登录猫：
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
答
您不能访问其他活动的变量这种方式，更好的方法（例如）是使用恒定类..
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;
}
}
主题：
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);
}
}
+0
好的。谢谢。我会试试这个.... – maestrosan11
+0
哦。伙计，你真棒。它现在有效.. – maestrosan11
错误是什么样的？也许'NullPointerEception'因为'main'没有被初始化？ – Howard
我在任何地方都看不到'main'的初始化。 –
这不是android的Activity类字段的工作方式。如果要将一个Activity的值传递给下一个，请使用键值对的Bundle或Intent。看看[这篇文章]（http://stackoverflow.com/q/6277662/593709） –