Android系统。 读取外部存储文件

Question

我尝试通过此程序从外部存储获取文件：

public class MainActivity extends Activity {

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

        TextView textView = findViewById(R.id.textView);
        StringBuilder builder = new StringBuilder();
        File specFile = Environment.getExternalStorageDirectory();

        builder.append(Environment.getExternalStorageState() + "\n");
        if (specFile.exists()) {
            builder.append(specFile);
            if (specFile.list() != null) {
                String[] files = specFile.list();
                for (int i = 0; i < files.length; i++) {
                    builder.append(files[i] +"\n");
                }
            } else {
                builder.append(" exist but empty\n");
            }
        }
        builder.append("/storage/emulated/0/Android exist: " + new File("/storage/emulated/0/Android").exists());
        textView.setText(builder);
    }
}

此权限已添加：

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

它在模拟器中效果很好，但是在真实电话中，当我尝试获取列表时它返回null。 它通常也可以在存储中找到目录。

Answer 1

通过添加以下代码解决了问题：

int requestCode = 0;

if (Build.VERSION.SDK_INT >= 23) {
    if(checkSelfPermission(Manifest.permission.READ_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED){
        requestPermissions(new String[]{Manifest.permission.READ_EXTERNAL_STORAGE}, requestCode);
    }
}