【发布时间】：2021-09-03 01:18:17
【问题描述】：
我正在创建一个应用程序来测试 listfiles() 方法是否正常工作以检查这个我创建了一个应用程序并在那里使用了 t 但这会返回 null 来代替数组。 这是我的完整代码，请帮忙，我已授予 android 11 的所有权限
MainActivity.java
package com.rajkumarcreations.file;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;
import androidx.core.content.ContextCompat;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.net.Uri;
import android.os.Build;
import android.os.Bundle;
import android.os.Environment;
import android.provider.Settings;
import android.widget.TextView;
import android.widget.Toast;
import org.w3c.dom.Text;
import java.io.File;
import static android.Manifest.permission.READ_EXTERNAL_STORAGE;
import static android.Manifest.permission.WRITE_EXTERNAL_STORAGE;
import static android.os.Build.VERSION.SDK_INT;
public class MainActivity extends AppCompatActivity {
TextView tv;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
tv = (TextView) findViewById(R.id.btn);
if(!checkPermission()){
requestPermission();
}else{
File file = new File(Environment.getExternalStorageDirectory()+"/Download/");
File[] allfiles = null;
allfiles = file.listFiles();
if(file.exists()){
tv.setText("Exist");
}
if(allfiles!=null){
Toast.makeText(this, "length is "+allfiles.length, Toast.LENGTH_SHORT).show();
}else{
Toast.makeText(this, "Array is null", Toast.LENGTH_SHORT).show();
}
}
}
private boolean checkPermission() {
if (SDK_INT >= Build.VERSION_CODES.R) {
return Environment.isExternalStorageManager();
} else {
int write = ContextCompat.checkSelfPermission(MainActivity.this, WRITE_EXTERNAL_STORAGE);
int read = ContextCompat.checkSelfPermission(MainActivity.this, READ_EXTERNAL_STORAGE);
return write == PackageManager.PERMISSION_GRANTED && read == PackageManager.PERMISSION_GRANTED;
}
}
private void requestPermission() {
if (SDK_INT >= Build.VERSION_CODES.R) {
try {
Intent intent = new Intent(Settings.ACTION_MANAGE_ALL_FILES_ACCESS_PERMISSION);
intent.addCategory("android.intent.category.DEFAULT");
intent.setData(Uri.parse(String.format("package:%s",new Object[]{getApplicationContext().getPackageName()})));
startActivityForResult(intent, 2000);
} catch (Exception e) {
Intent intent = new Intent();
intent.setAction(Settings.ACTION_MANAGE_ALL_FILES_ACCESS_PERMISSION);
startActivityForResult(intent, 2000);
}
} else {
ActivityCompat.requestPermissions(MainActivity.this, new String[]{WRITE_EXTERNAL_STORAGE,READ_EXTERNAL_STORAGE}, 333);
}
}
@Override
protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if (requestCode == 2000) {
if (SDK_INT >= Build.VERSION_CODES.R) {
if (Environment.isExternalStorageManager()) {
Toast.makeText(this, "Allow permissions granted", Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(this, "Allow permission for storage access!", Toast.LENGTH_SHORT).show();
}
}
}
}
@Override
public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
super.onRequestPermissionsResult(requestCode,permissions,grantResults);
if (requestCode==333){
if (grantResults.length > 0) {
boolean WRITE_EXTERNAL_STORAGE = grantResults[0] == PackageManager.PERMISSION_GRANTED;
boolean READ_EXTERNAL_STORAGE = grantResults[1] == PackageManager.PERMISSION_GRANTED;
if (READ_EXTERNAL_STORAGE && WRITE_EXTERNAL_STORAGE) {
Toast.makeText(this, "All permissions granted", Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(this, "Allow permission for storage access!", Toast.LENGTH_SHORT).show();
}
}
}
}
}
清单文件
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.rajkumarcreations.file">
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE"/>
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:requestLegacyExternalStorage="true"
android:theme="@style/AppTheme">
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
XML 文件
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hello World!"
android:id="@+id/btn"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
【问题讨论】：
-
folder.listfiles() is returning null为哪个目录？ -
试试
File file = Environment.getExternalStorageDirectory();在Android 11 设备上，您可以列出外部存储的根目录，您将获得所有公共目录。 （也下载）。 ` 这样做不需要任何许可。 -
您确定返回的是 null 而不是空数组？因为我宁愿期待一个空数组。
-
folder.listfiles() 正在为每个目录返回
-
?????????????????????退货是什么？
标签： java android android-11