Android 更改活动时应用程序崩溃

我一直致力于在我的应用程序中支持多个屏幕。但是，当我的屏幕被检测为480x800屏幕时，它会切换到该分辨率的活动，但此时它会崩溃

这是detect.java，它根据屏幕分辨率做出决定：

package com.example.mywallpapers;

import android.app.Activity;
import android.content.Intent;
import android.graphics.Point;
import android.os.Build;
import android.os.Bundle;
import android.view.Display;
import android.view.WindowManager;

public class Detect extends Activity {

    @SuppressWarnings("deprecation")
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        int width = 0;
        Point size = new Point();
        WindowManager w = getWindowManager();

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB_MR2) {

            w.getDefaultDisplay().getSize(size);

            width = size.x;
        } else {
            Display d = w.getDefaultDisplay();
            width = d.getWidth();
        }
        if (width == 480) {
                startActivity(new Intent(Detect.this, SevenTwentyOne.class));



        } else if (width == 720) {
            startActivity(new Intent("com.example.mywallpapers.FOUREIGHTONE"));
        } else {
            startActivity(new Intent("com.example.mywallpapers.FOUREIGHTONE"));
        }

    }



    }

这是我的第七十二个类（不是针对1280x720分辨率，而是针对480x800）

每当我在480x800手机上测试我的应用程序时，它都会因NullPointerExection而崩溃。你知道那是从哪里来的吗

这是logCat：

05-15 11:27:47.600: E/AndroidRuntime(31642): FATAL EXCEPTION: main
05-15 11:27:47.600: E/AndroidRuntime(31642): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.mywallpapers/com.example.mywallpapers.SevenTwentyOne}: java.lang.NullPointerException
05-15 11:27:47.600: E/AndroidRuntime(31642):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2100)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2125)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at android.app.ActivityThread.access$600(ActivityThread.java:140)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1227)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at android.os.Handler.dispatchMessage(Handler.java:99)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at android.os.Looper.loop(Looper.java:137)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at android.app.ActivityThread.main(ActivityThread.java:4898)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at java.lang.reflect.Method.invokeNative(Native Method)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at java.lang.reflect.Method.invoke(Method.java:511)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1008)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:775)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at dalvik.system.NativeStart.main(Native Method)
05-15 11:27:47.600: E/AndroidRuntime(31642): Caused by: java.lang.NullPointerException
05-15 11:27:47.600: E/AndroidRuntime(31642):    at com.example.mywallpapers.SevenTwentyOne.onCreate(SevenTwentyOne.java:90)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at android.app.Activity.performCreate(Activity.java:5206)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2064)
05-15 11:27:47.600: E/AndroidRuntime(31642):    ... 11 more

---

logcat中的空指针在SevenTwentyOne.java中的第90行，你能突出显示那一行吗？发布你的“四八八分之一”布局文件你的布局文件中有按钮Wap50吗对不起，这是不可能的，如果没有xml，我会在问题正文中获得太多字符，最可能的答案是@Iftikar Urrhman Khan评论。Wap50不在布局中，因为如果找不到视图，findViewById（）将返回null。

05-15 11:27:47.600: E/AndroidRuntime(31642): FATAL EXCEPTION: main
05-15 11:27:47.600: E/AndroidRuntime(31642): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.mywallpapers/com.example.mywallpapers.SevenTwentyOne}: java.lang.NullPointerException
05-15 11:27:47.600: E/AndroidRuntime(31642):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2100)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2125)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at android.app.ActivityThread.access$600(ActivityThread.java:140)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1227)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at android.os.Handler.dispatchMessage(Handler.java:99)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at android.os.Looper.loop(Looper.java:137)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at android.app.ActivityThread.main(ActivityThread.java:4898)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at java.lang.reflect.Method.invokeNative(Native Method)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at java.lang.reflect.Method.invoke(Method.java:511)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1008)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:775)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at dalvik.system.NativeStart.main(Native Method)
05-15 11:27:47.600: E/AndroidRuntime(31642): Caused by: java.lang.NullPointerException
05-15 11:27:47.600: E/AndroidRuntime(31642):    at com.example.mywallpapers.SevenTwentyOne.onCreate(SevenTwentyOne.java:90)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at android.app.Activity.performCreate(Activity.java:5206)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094)
05-15 11:27:47.600: E/AndroidRuntime(31642):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2064)
05-15 11:27:47.600: E/AndroidRuntime(31642):    ... 11 more