我尝试遵循一位名为Pixel_95的Youtuber的例子关于文件的读写。它使用写入外部设备的权限。
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
然后
public String path = Environment.getExternalStorageDirectory().getAbsolutePath() + "/readWriteTutorial";
这将创建一个路径“/storage/emulated/0/readWriteTutorial”。在 onCreate() 中。我把
File dir = new File(path);
dir.mkdirs();
但是,我的设备上没有这样的文件夹。使用我的三星 S7 中的文件管理器应用程序时,任何地方都没有/storage/emulated。因此,当它尝试运行时:
FileOutputStream fos = null;
fos = new FileOutputStream(file);
在 Save() 方法中。异常被捕获。
FATAL EXCEPTION: main
Process: com.example.jiajunyang.readwrite, PID: 1170
java.lang.IllegalStateException: Could not execute method for android:onClick
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:293)
at android.view.View.performClick(View.java:6213)
at android.widget.TextView.performClick(TextView.java:11074)
at android.view.View$PerformClick.run(View.java:23645)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6692)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1468)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1358)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Method.invoke(Native Method)
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)
at android.view.View.performClick(View.java:6213)
at android.widget.TextView.performClick(TextView.java:11074)
at android.view.View$PerformClick.run(View.java:23645)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6692)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1468)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1358)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void java.io.FileOutputStream.close()' on a null object reference
at com.example.jiajunyang.readwrite.MainActivity.Save(MainActivity.java:161)
at com.example.jiajunyang.readwrite.MainActivity.onSaveClicked(MainActivity.java:111)
at java.lang.reflect.Method.invoke(Native Method)
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)
at android.view.View.performClick(View.java:6213)
at android.widget.TextView.performClick(TextView.java:11074)
at android.view.View$PerformClick.run(View.java:23645)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6692)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1468)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1358)
主要是这个:
java.lang.NullPointerException: Attempt to invoke virtual method 'void java.io.FileOutputStream.close()' on a null object reference
那么有什么办法可以解决这个问题呢?我似乎无法获得正确的路径来创建目录。非常感谢您的帮助。
最佳答案
使用Context.getExternalFilesDirs(null)
,您将能够检索设备上存在的外部目录。然后,您将能够检查“storage/emulated/0”是否出现在列表中。
关于java - Android Studio,/storage/emulated/0 不存在,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/48478182/