由java.lang.NullPointerException引起:尝试调用虚拟方法';intandroid.graphics.Bitmap.getWidth()';关于空对象引用
我有BitmapScalingHelper.java:由java.lang.NullPointerException引起:尝试调用虚拟方法';intandroid.graphics.Bitmap.getWidth()';关于空对象引用,android,android-activity,nullpointerexception,android-bitmap,Android,Android Activity,Nullpointerexception,Android Bitmap,我有BitmapScalingHelper.java: public class BitmapScalingHelper { public static Bitmap decodeResource(Resources res, int resId, int dstWidth, int dstHeight) { Options options = new Options(); options.inJustDecodeBounds = true;
public class BitmapScalingHelper
{
public static Bitmap decodeResource(Resources res, int resId, int dstWidth, int dstHeight)
{
Options options = new Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeResource(res, resId, options);
options.inJustDecodeBounds = false;
options.inSampleSize = calculateSampleSize(options.outWidth, options.outHeight, dstWidth,
dstHeight);
Bitmap unscaledBitmap = BitmapFactory.decodeResource(res, resId, options);
return unscaledBitmap;
}
public static Bitmap decodeFile(String filePath, int dstWidth, int dstHeight)
{
Options options = new Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeFile(filePath, options);
options.inJustDecodeBounds = false;
options.inSampleSize = calculateSampleSize(options.outWidth, options.outHeight, dstWidth,
dstHeight);
Bitmap unscaledBitmap = BitmapFactory.decodeFile(filePath, options);
return unscaledBitmap;
}
public static int calculateSampleSize(int srcWidth, int srcHeight, int dstWidth, int dstHeight)
{
final float srcAspect = (float)srcWidth / (float)srcHeight;
final float dstAspect = (float)dstWidth / (float)dstHeight;
if (srcAspect > dstAspect)
{
return srcWidth / dstWidth;
}
else
{
return srcHeight / dstHeight;
}
}
public static Bitmap createScaledBitmap(Bitmap unscaledBitmap, int dstWidth, int dstHeight)
{
Rect srcRect = calculateSrcRect(unscaledBitmap.getWidth(), unscaledBitmap.getHeight());
Rect dstRect = calculateDstRect(unscaledBitmap.getWidth(), unscaledBitmap.getHeight(),
dstWidth, dstHeight);
Bitmap scaledBitmap = Bitmap.createBitmap(dstRect.width(), dstRect.height(),
Config.ARGB_8888);
Canvas canvas = new Canvas(scaledBitmap);
canvas.drawBitmap(unscaledBitmap, srcRect, dstRect, new Paint(Paint.FILTER_BITMAP_FLAG));
return scaledBitmap;
}
public static Rect calculateSrcRect(int srcWidth, int srcHeight)
{
System.out.print("Scr" + srcWidth + " " + srcHeight);
return new Rect(0, 0, srcWidth, srcHeight);
}
public static Rect calculateDstRect(int srcWidth, int srcHeight, int dstWidth, int dstHeight)
{
final float srcAspect = (float)srcWidth / (float)srcHeight;
final float dstAspect = (float)dstWidth / (float)dstHeight;
if (srcAspect > dstAspect)
{
return new Rect(0, 0, dstWidth, (int)(dstWidth / srcAspect));
}
else
{
return new Rect(0, 0, (int)(dstHeight * srcAspect), dstHeight);
}
}
}
在这一类中有:
createScaledBitmap()
…返回缩放的位图图像
在另一个类中,我有以下方法:
public Bitmap readSelectedBitmapFromFile(Context context, String fileName)
{
DisplayMetrics metrics = new DisplayMetrics();
WindowManager windowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
windowManager.getDefaultDisplay().getMetrics(metrics);
Bitmap scaledBitmap = getDefaultBitmap(context);
try {
File themeParentDir = context.getDir(THEME_DIRECTORY_NAME, Context.MODE_PRIVATE); //Creating an internal dir;
File themeSubDir = new File(themeParentDir, THEME_SUB_DIRECTORY_NAME + getThemeBasedDirectoryNumber(m_SelectedTheme));
themeSubDir.mkdir();
File themeFileWithinDir = new File(themeSubDir, fileName); //Getting a file within the dir.
if(themeFileWithinDir.exists())
{
// Part 1: Decode image
Bitmap unscaledBitmap = BitmapScalingHelper.decodeFile(themeFileWithinDir.getPath(), metrics.widthPixels, metrics.heightPixels);
// Part 2: Scale image
scaledBitmap = BitmapScalingHelper.createScaledBitmap(unscaledBitmap, metrics.widthPixels, metrics.heightPixels);
unscaledBitmap.recycle();
}
m_SelectedBitmap = scaledBitmap;
}
catch (Error e) {
e.printStackTrace();
}
return scaledBitmap;
}
这段代码在许多设备中运行良好。但它在某些设备上崩溃了。谁能帮我一下吗
我得到的日志如下:
Fatal Exception: java.lang.RuntimeException: Unable to start activity ComponentInfo: java.lang.NullPointerException: Attempt to invoke virtual method 'int android.graphics.Bitmap.getWidth()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3254)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3350)
at android.app.ActivityThread.access$1100(ActivityThread.java:222)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1795)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:158)
at android.app.ActivityThread.main(ActivityThread.java:7229)
at java.lang.reflect.Method.invoke(Method.java)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
Caused by java.lang.NullPointerException: Attempt to invoke virtual method 'int android.graphics.Bitmap.getWidth()' on a null object reference
at in.plackal.lovecyclesfree.util.BitmapScalingHelper.createScaledBitmap(SourceFile:62)
at in.plackal.lovecyclesfree.general.ThemeManager.readSelectedBitmapFromFile(SourceFile:202)
at in.plackal.lovecyclesfree.activity.SplashActivity.onCreate(SourceFile:70)
at android.app.Activity.performCreate(Activity.java:6876)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1135)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3207)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3350)
at android.app.ActivityThread.access$1100(ActivityThread.java:222)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1795)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:158)
at android.app.ActivityThread.main(ActivityThread.java:7229)
at java.lang.reflect.Method.invoke(Method.java)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
如果是权限问题,它不应该在Android-M版本以下崩溃,但在一些Android-M之前的设备上也会崩溃。您正在使用:
位图解码文件(字符串路径名)
如果文件解码失败,此方法可能返回null。
我认为这可能与某些设备上的权限问题或不支持的图像格式有关。
如果您使用的是GIF,请尝试可能有一些原因会导致此错误
您面临的问题是,您正试图在
createScaledBitmap
函数中的unscaledBitmap
上执行getWidth()
。显然,您的unscaledBitmap
有时是null
;调用getWidth()
会导致空指针异常
根本原因是无论出于何种原因,decodeResource
都会返回空值
原因可能包括-
decodeResource
时被不同地解释。您可以尝试在那里传递null
修改后的代码应如下所示-
public class BitmapScalingHelper
{
public static Bitmap decodeResource(Resources res, int resId, int dstWidth, int dstHeight)
{
Options options = new Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeResource(res, resId, options);
options.inJustDecodeBounds = false;
options.inSampleSize = calculateSampleSize(options.outWidth, options.outHeight, dstWidth,
dstHeight);
options = new Options();
//May use null here as well. The funciton may interpret the pre-used options variable in ways hard to tell.
Bitmap unscaledBitmap = BitmapFactory.decodeResource(res, resId, options);
if(unscaledBitmap == null)
{
Log.e("ERR","Failed to decode resource - " + resId + " " + res.toString());
return null;
}
return unscaledBitmap;
}
}
如果您使用创建不好的库jar,并且在gradle上将minifyEnabled设置为true,也可能导致此错误。简单回答: 按照以下步骤操作
好吧,我反复遇到这个错误,我解决这个问题的方法是确保使用.png图像作为位图图像,并将其保存在drawable文件夹中。以前我把它作为向量资产使用。
这对我来说很好。对于Android 10,将这一行添加到清单中:
android:requestLegacyExternalStorage="true"
请注意,您还必须添加所需的基本任务:
读外部存储器,写外部存储器
但是kitkat(4.4.4)中的程序也崩溃了。请提供清单权限以及如何将文件编码到主题目录名称?哪一行导致了异常(来自方法而不是整个类。)@PavanBilagi您找到了更好的内存管理解决方案吗,我发现在xperia xa中,这种情况几乎每次都会发生。但是如果您在调试模式下,在按f9之前在解码文件上稍等片刻,它就会工作。而且在几乎所有其他设备上都能正常工作。我也在用一些和你一样的东西。如果我把这一行放在其他android版本中会发生什么?