File.createNewFile()方法在Android M中引发异常 [英] File.createNewFile() method throws exception in Android M

问题描述

我无法在Android M中创建文件.

I have a problem to create file in Android M.

我在 Android 6.0.1 上使用了 Nexus 9 .然后，在我的项目中进行如下设置:

I use Nexus 9 with Android 6.0.1. Then I set in my project as below:

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

build.gradle

android {
    defaultConfig {
        targetSdkVersion 23
        ...
    }
}

MainActivity.Java

public class MainActivity extends AppCompatActivity {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    String storagePath = Environment.getExternalStorageDirectory().getAbsolutePath();
    String rootPath = storagePath + "/test";
    String fileName = "/test.zip";

    File root = new File(rootPath);
    if(!root.mkdirs()) {
        Log.i("Test", "This path is already exist: " + root.getAbsolutePath());
    }

    File file = new File(rootPath + fileName);
    try {
        if (!file.createNewFile()) {
            Log.i("Test", "This file is already exist: " + file.getAbsolutePath());
        }

    } catch (Exception e) {
        e.printStackTrace();
    }
}

构建成功并且启动了应用程序，但是我收到了如下异常消息:

Build was success and application was launched, but I got exception message like this:

01-07 18:13:40.669 18027-18027/com.sample.myapplication W/System.err: java.io.IOException: open failed: ENOENT (No such file or directory)
01-07 18:13:40.669 18027-18027/com.sample.myapplication W/System.err:     at java.io.File.createNewFile(File.java:939)
01-07 18:13:40.669 18027-18027/com.sample.myapplication W/System.err:     at com.sample.myapplication.MainActivity.onCreate(MainActivity.java:36)
01-07 18:13:40.670 18027-18027/com.sample.myapplication W/System.err:     at android.app.Activity.performCreate(Activity.java:6251)
01-07 18:13:40.670 18027-18027/com.sample.myapplication W/System.err:     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
01-07 18:13:40.670 18027-18027/com.sample.myapplication W/System.err:     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
01-07 18:13:40.670 18027-18027/com.sample.myapplication W/System.err:     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
01-07 18:13:40.670 18027-18027/com.sample.myapplication W/System.err:     at android.app.ActivityThread.-wrap11(ActivityThread.java)
01-07 18:13:40.671 18027-18027/com.sample.myapplication W/System.err:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
01-07 18:13:40.671 18027-18027/com.sample.myapplication W/System.err:     at android.os.Handler.dispatchMessage(Handler.java:102)
01-07 18:13:40.671 18027-18027/com.sample.myapplication W/System.err:     at android.os.Looper.loop(Looper.java:148)
01-07 18:13:40.671 18027-18027/com.sample.myapplication W/System.err:     at android.app.ActivityThread.main(ActivityThread.java:5417)
01-07 18:13:40.671 18027-18027/com.sample.myapplication W/System.err:     at java.lang.reflect.Method.invoke(Native Method)
01-07 18:13:40.671 18027-18027/com.sample.myapplication W/System.err:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
01-07 18:13:40.671 18027-18027/com.sample.myapplication W/System.err:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
01-07 18:13:40.671 18027-18027/com.sample.myapplication W/System.err: Caused by: android.system.ErrnoException: open failed: ENOENT (No such file or directory)
01-07 18:13:40.671 18027-18027/com.sample.myapplication W/System.err:     at libcore.io.Posix.open(Native Method)
01-07 18:13:40.671 18027-18027/com.sample.myapplication W/System.err:     at libcore.io.BlockGuardOs.open(BlockGuardOs.java:186)
01-07 18:13:40.671 18027-18027/com.sample.myapplication W/System.err:     at java.io.File.createNewFile(File.java:932)
01-07 18:13:40.671 18027-18027/com.sample.myapplication W/System.err:   ... 13 more

我该如何解决这个问题?我不明白我想念的是什么...

How can I solve this problem? I don't catch what I miss....

请帮助.

推荐答案

已更新

替换storagePath以访问适用于Android 10的作用域存储.

Updated

Replace storagePath to access scoped storage, for Android 10.

有关更多详细信息，请参考文档.

Refer this document for more detail.

谢谢，拉尔托.

我不知道运行时权限.

我这样解决了异常:

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        /* Request user permissions in runtime */
        ActivityCompat.requestPermissions(MainActivity.this,
                new String[] {
                        Manifest.permission.READ_EXTERNAL_STORAGE,
                        Manifest.permission.WRITE_EXTERNAL_STORAGE
                },
                100);
        /* Request user permissions in runtime */

        createTestFile();
    }

    @TargetApi(23)
    @Override
    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
        switch (requestCode) {
            case 100:
                if (grantResults.length > 0
                        && grantResults[0] == PackageManager.PERMISSION_GRANTED
                        && grantResults[1] == PackageManager.PERMISSION_GRANTED) {
                    // User checks permission.

                } else {
                    Toast.makeText(MainActivity.this, "Permission is denied.", Toast.LENGTH_SHORT).show();
                    finish();
                }
        }
    }

    private void createTestFile() {
        // String storagePath = Environment.getExternalStorageDirectory().getAbsolutePath();

        // If Target API level is 29(Android 10),
        // you should access local path in scoped storage mode.
        File localStorage = getExternalFilesDir(null);
        if (localStorage == null) { return; }
        String storagePath = localStorage.getAbsolutePath();
        String rootPath = storagePath + "/test";
        String fileName = "/test.zip";

        File root = new File(rootPath);
        if(!root.mkdirs()) {
            Log.i("Test", "This path is already exist: " + root.getAbsolutePath());
        }

        File file = new File(rootPath + fileName);
        try {
            int permissionCheck = ContextCompat.checkSelfPermission(
                    MainActivity.this,
                    android.Manifest.permission.WRITE_EXTERNAL_STORAGE);
            if (permissionCheck == PackageManager.PERMISSION_GRANTED) {
                if (!file.createNewFile()) {
                    Log.i("Test", "This file is already exist: " + file.getAbsolutePath());
                }
            }

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

有效！

这篇关于File.createNewFile()方法在Android M中引发异常的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！