Question

我尝试按照名为Pixel_95的Youtuber关于读写文件的示例。它使用权限写入外部设备。

<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";

这会创建一个路径为＆＃34; / storage / emulated / 0 / readWriteTutorial＆＃34;。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Samsung S7中的文件管理器应用程序在任何地方都没有/存储/模拟。所以当它试图运行时：

FileOutputStream fos = null;
fos = new FileOutputStream(file);

在Save（）方法中。抓住了例外。

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：

java.lang.NullPointerException: Attempt to invoke virtual method 'void java.io.FileOutputStream.close()' on a null object reference

那么解决方案是什么？我似乎无法获得制作目录的正确途径。非常感谢您的帮助。

Answer 1

使用Context.getExternalFilesDirs(null)，您将能够检索设备上存在哪个外部目录。然后，您将能够检查列表中是否显示“storage / emulated / 0”。

Android studio，/ storage / emulated / 0不存在

1 个答案: