Java 为什么我的应用程序出现不支持的URI内容错误？

我正在尝试编写一个Android应用程序，需要查询用户以选择一些数据文件所在的目录

当执行以下代码时，Android文件选择器启动，我选择一个目录

返回的URI在我看来是有效的：

content://com.android.externalstorage.documents/tree/primary%3ANotifications

然后，当我查询内容提供者时，它崩溃了

返回的错误如下：

这是我的密码：

package com.muddco.fptest2;

import androidx.appcompat.app.AppCompatActivity;

import android.content.ContentResolver;
import android.content.Intent;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    static String TAG = "TEST123";
    public static TextView textView, uriView;
    public  Object act = this;

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

        textView = (TextView) findViewById(R.id.view1);
        uriView = (TextView) findViewById(R.id.uriview);;

        showFileChooser();
    }

    private static final int FILE_SELECT_CODE = 0;

    private void showFileChooser() {
        Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT_TREE);
        intent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
        intent.addCategory(Intent.CATEGORY_DEFAULT);
        try {
            startActivityForResult(
                    Intent.createChooser(intent, "Select a Directory"),
                    FILE_SELECT_CODE);
        } catch (android.content.ActivityNotFoundException ex) {
            // Potentially direct the user to the Market with a Dialog
            Toast.makeText(this, "Please install a File Manager.", Toast.LENGTH_SHORT).show();
        }
    }

    @Override
     protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        switch (requestCode) {
            case FILE_SELECT_CODE:
                if (resultCode == RESULT_OK) {
                    // Get the Uri of the selected file
                    Uri uri = data.getData();
                    Log.d(TAG, "File Uri: " + uri.toString());
                    uriView.setText("URI: "+ uri.toString());

                    final int takeFlags = data.getFlags()
                            & (Intent.FLAG_GRANT_READ_URI_PERMISSION
                            | Intent.FLAG_GRANT_WRITE_URI_PERMISSION);

                    getContentResolver().takePersistableUriPermission(uri, takeFlags);
                    ContentResolver contentResolver = getContentResolver();
                    String[] projection = { "*" };

                    Cursor cursor = contentResolver.query(uri,projection,null,null, null  );

                    // We never get here - the query crashes with an Unsuported URI content error

                    if(cursor!=null) {

                        TextView pathView = (TextView) findViewById(R.id.pathView);
                        pathView.setText("URI: ");

                        cursor.moveToFirst();

                        // Loop in the cursor to get each row.
                        do {
                            // Get column 1 value.
                            int column1Index = cursor.getColumnIndex("column1");
                            String column1Value = cursor.getString(column1Index);

                            // Get column 2 value.
                            int column2Index = cursor.getColumnIndex("column2");
                            String column2Value = cursor.getString(column2Index);

                            pathView.setText(pathView.getText() + column1Value + " | " + column2Value + "\n");

                        } while (cursor.moveToNext());
                    }


                    //Toast.makeText(this, "File Uri: " + uri.toString(),
                    //        Toast.LENGTH_LONG).show();
                    // Get the path
                    // Get the file instance
                    // File file = new File(path);
                    // Initiate the upload
                }
                break;
        }
        super.onActivityResult(requestCode, resultCode, data);
    }
}

我在清单中设置了以下权限：

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

请原谅我糟糕的编码，因为我正在学习Android编程

任何关于如何使thw正确工作的建议都将不胜感激

---

谢谢

多亏了使用Commonware，我才成功地使事情运转起来

以下是工作代码：

package com.muddco.fl99;

import android.content.Context;
import android.os.Bundle;
import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.net.Uri;
import android.util.Log;
import android.widget.TextView;
import android.widget.Toast;;
import androidx.documentfile.provider.DocumentFile;


public class MainActivity extends AppCompatActivity {

    static String TAG = "TEST123";
    public static TextView fileView, uriView;
    public Context act = this;

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

        fileView = (TextView) findViewById(R.id.fileView);
        uriView = (TextView) findViewById(R.id.uriView);;

        showFileChooser();
    }

    private static final int FILE_SELECT_CODE = 0;

    private void showFileChooser() {
        Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT_TREE);
        intent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
        intent.addCategory(Intent.CATEGORY_DEFAULT);
        try {
            startActivityForResult(
                    Intent.createChooser(intent, "Select a Directory"),
                    FILE_SELECT_CODE);
        } catch (android.content.ActivityNotFoundException ex) {
            // Potentially direct the user to the Market with a Dialog
            Toast.makeText(this, "Please install a File Manager.", Toast.LENGTH_SHORT).show();
        }
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        switch (requestCode) {
            case FILE_SELECT_CODE:
                if (resultCode == RESULT_OK) {
                    // Get the Uri of the selected file
                    Uri uri = data.getData();
                    Log.d(TAG, "File Uri: " + uri.toString());
                    uriView.setText("URI: "+ uri.toString());

                    DocumentFile dfile = DocumentFile.fromTreeUri(act, uri);
                    DocumentFile[] fileList = dfile.listFiles();
                    Log.d(TAG,fileList.toString() );
                    int jj=1;

                    for (DocumentFile docfile : fileList) {

                        Log.d(TAG, "File: " + docfile.getUri() + "\n");
                    }
                }
                break;
        }
        super.onActivityResult(requestCode, resultCode, data);
    }


}

---

这不是使用文档

Uri

的方式。您试图用该

Uri

实现什么？我试图访问一个目录以获取它包含的文件列表。调用

DocumentFile.fromTreeUri（）

，传入您的树

Uri

。调用

DocumentFile

上的

listFiles（）

以获取该树的内容。我需要包括哪些内容才能识别DocumentFile类？不管怎样，我已经解决了。配置错误…您似乎完全抛弃了内容解析程序代码。SAF确实没有使用内容解析器，而且我们必须依赖于特殊的访问方法，如

fromTreeUri（）

？值得注意的是，for

文档文件

特别指出，它是

文档契约

的简化抽象，开销很大。如果可能，您应该只使用后者。要了解如何做到这一点，您可以查看

DocumentFile

的实现，它非常简单。

package com.muddco.fl99;

import android.content.Context;
import android.os.Bundle;
import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.net.Uri;
import android.util.Log;
import android.widget.TextView;
import android.widget.Toast;;
import androidx.documentfile.provider.DocumentFile;


public class MainActivity extends AppCompatActivity {

    static String TAG = "TEST123";
    public static TextView fileView, uriView;
    public Context act = this;

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

        fileView = (TextView) findViewById(R.id.fileView);
        uriView = (TextView) findViewById(R.id.uriView);;

        showFileChooser();
    }

    private static final int FILE_SELECT_CODE = 0;

    private void showFileChooser() {
        Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT_TREE);
        intent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
        intent.addCategory(Intent.CATEGORY_DEFAULT);
        try {
            startActivityForResult(
                    Intent.createChooser(intent, "Select a Directory"),
                    FILE_SELECT_CODE);
        } catch (android.content.ActivityNotFoundException ex) {
            // Potentially direct the user to the Market with a Dialog
            Toast.makeText(this, "Please install a File Manager.", Toast.LENGTH_SHORT).show();
        }
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        switch (requestCode) {
            case FILE_SELECT_CODE:
                if (resultCode == RESULT_OK) {
                    // Get the Uri of the selected file
                    Uri uri = data.getData();
                    Log.d(TAG, "File Uri: " + uri.toString());
                    uriView.setText("URI: "+ uri.toString());

                    DocumentFile dfile = DocumentFile.fromTreeUri(act, uri);
                    DocumentFile[] fileList = dfile.listFiles();
                    Log.d(TAG,fileList.toString() );
                    int jj=1;

                    for (DocumentFile docfile : fileList) {

                        Log.d(TAG, "File: " + docfile.getUri() + "\n");
                    }
                }
                break;
        }
        super.onActivityResult(requestCode, resultCode, data);
    }


}