如何解决将位图压缩为JPEG时为什么会出现空指针异常?
我正在尝试将我的位图图像存储到Items目录中的jpeg文件中。但是,当尝试使用compress ()
将位图压缩为JPEG时,会收到空指针异常。我尝试调试,但发现尝试创建的Items目录失败,因此未创建任何目录。此外,位图也不为空。
我似乎找不到关于为什么未创建目录的问题,并且不知道这是压缩位图时是否得到空指针异常的原因。我尝试过请求存储权限,但这不能解决问题。
更新 :我现在已经能够创建Items目录,但是在压缩位图时仍然会出现空指针异常。
试图将位图保存到Items目录的代码:
public void saveBitmap () {
boolean dirCreated;
askForPermission(Manifest.permission.WRITE_EXTERNAL_STORAGE,STORAGE_PERMISSION_CODE);
File filePath = Environment.getExternalStorageDirectory ();
File dir = new File (filePath.getAbsolutePath() + "/Items");
if (!dir.exists ()) {
try {
dirCreated = dir.mkdir();
if (!dirCreated) {
Log.d ("notCreated","the directory has failed");
}
} catch (SecurityException e) {
e.printStackTrace();
}
} else {
Log.d ("dirExists","the directory already exists");//I receive this in the Log cat
}
file = new File (dir,name + ".jpg");
Log.d ("filey","file has been created");//I receive this in the log cat
try {
outputStream = new FileOutputStream(file);
} catch (FileNotFoundException e) {
e.printStackTrace ();
}
if (bitmap != null) {
Log.d ("bitty","the bimap is not null");//I receive this in the log cat
}
bitmap.compress (Bitmap.CompressFormat.JPEG,outputStream);
}
将我的资源转换为位图的代码:
public void convertToBitmap () {
bitmap = BitmapFactory.decodeResource(context.getResources(),resourceId);
}
要求存储权限的代码:
public void askForPermission (String permission,int requestCode) {
if (isStoragePermissionGranted()) {
ActivityCompat.requestPermissions((Activity) context,new String [] {permission},requestCode);
} else {
Toast.makeText (context,"Permission already granted",Toast.LENGTH_SHORT)
.show();
}
}
public void onRequestPermissionsResult (int requestCode,String [] permissions,int [] grantResults) {
super.onRequestPermissionsResult (requestCode,permissions,grantResults);
if (requestCode == STORAGE_PERMISSION_CODE) {
if (grantResults.length > 0 && grantResults [0] == PackageManager.PERMISSION_GRANTED) {
Toast.makeText(context,"Storage Permission Granted",Toast.LENGTH_SHORT);
} else {
Toast.makeText(context,"Storage Permission Denied",Toast.LENGTH_SHORT);
}
}
}
public boolean isStoragePermissionGranted () {
if (ContextCompat.checkSelfPermission(context,Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
Toast.makeText(context,"permission granted",Toast.LENGTH_SHORT)
.show();
return true;
}
return false;
}
清单文件:
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
我收到的错误:
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.myapps.myapplication/com.myapps.myapplication.grocery_item}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3374)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3513)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2109)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7682)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:516)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950)
Caused by: java.lang.NullPointerException
at android.graphics.Bitmap.compress(Bitmap.java:1407)
at com.myapps.myapplication.BitmapFiles.saveBitmap(BitmapFiles.java:86) //THIS IS THE LINE OF CODE CAUSING THE EXCEPTION
at com.myapps.myapplication.BitmapFiles.<init>(BitmapFiles.java:40)
at com.myapps.myapplication.MyDatabaseHelper.createBitmapFiles(MyDatabaseHelper.java:40)
at com.myapps.myapplication.MyDatabaseHelper.upgradeDatabase(MyDatabaseHelper.java:35)
at com.myapps.myapplication.MyDatabaseHelper.onUpgrade(MyDatabaseHelper.java:63)
at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:417)
at android.database.sqlite.SQLiteOpenHelper.getReadableDatabase(SQLiteOpenHelper.java:341)
at com.myapps.myapplication.grocery_item.accessDataBase(grocery_item.java:35)
at com.myapps.myapplication.grocery_item.onCreate(grocery_item.java:20)
at android.app.Activity.performCreate(Activity.java:7815)
at android.app.Activity.performCreate(Activity.java:7804)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1318)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3349)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3513)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2109)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7682)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:516)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950)
解决方法
检查以确保outputStream
不为空,如果输出流为空,请检查compress() will throw a NullPointerException()。
正如我在Null Pointer Exception when trying to compress Bitmap中看到的那样,您需要执行以下操作:
app.UseMvc(routes =>
{
routes.MapRoute(
name: "default",template: "{controller=Home}/{action=Index}/{id?}");
routes.MapRoute(
name: "default",template: "{id?}",new { controller = "Home",action = "Index" });
});
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