java - 显示特定目录中的所有图像

Question

我是安卓新手。尝试创建一个应用程序，允许用户下载图片，然后将其存储在外部存储中，我的代码工作正常，但它显示了外部存储的所有图像。我将这些图片存储在设备上的特定文件夹中，但我不知道如何显示该文件夹中所有图片的列表。

like /storage/emulated/0/due/image/ only show this location pictures.

If I write an image path, the application crashes.

我的代码

public class mainActivity extends AppCompatActivity  {
GridView gridView;
ArrayList<File> list;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);




        checkPermissions();

        list = getImageFiles(new File(Environment.getExternalStorageDirectory().getPath() + " /storage/emulated/0/due/image/"));

        gridView = (GridView) findViewById(R.id.gridView);
        gridView.setAdapter(new GridAdapter());

        gridView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
              //  startActivity(new Intent(getApplicationContext(), ViewImage.class).putExtra("img", list.get(i).toString()));
            }
        });

    }

    class GridAdapter extends BaseAdapter {

        @Override
        public int getCount() {
            return list.size();
        }

        @Override
        public Object getItem(int i) {
            return list.get(i);
        }

        @Override
        public long getItemId(int i) {
            return 0;
        }

        @Override
        public View getView(int i, View view, ViewGroup viewGroup) {
            view = getLayoutInflater().inflate(R.layout.image_loader_list_item, viewGroup, false);
            ImageView imageView = (ImageView) view.findViewById(R.id.imageView);
            //imageview.setImageURI(Uri.parse(getItem(i).toString()));

            //Loading image from below url into imageView
            Glide.with(getApplicationContext())
                    .load(getItem(i).toString())
                    .into(imageView);
            return view;
        }
    }

    ArrayList<File> getImageFiles(File root) {
        ArrayList<File> list = new ArrayList();
        File[] files = root.listFiles();
        for (int i = 0; i < files.length; i++) {
            if(files[i].isDirectory()) {
                list.addAll(getImageFiles(files[i]));
            } else {
                if(files[i].getName().endsWith(".jpg") || files[i].getName().endsWith(".png") || files[i].getName().endsWith(".gif")) {
                    list.add(files[i]);
                }
            }
        }
        return  list;
    }

    private void checkPermissions(){
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            if(checkSelfPermission(Manifest.permission.READ_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED){
                //Requesting permission.
                ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.READ_EXTERNAL_STORAGE}, 1);
            }
        }
    }

    @Override //Override from ActivityCompat.OnRequestPermissionsResultCallback Interface
    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
        switch (requestCode) {
            case 1: {
                // If request is cancelled, the result arrays are empty.
                if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    // permission granted
                }
                return;
            }
        }
    }

    private ActivityManager.MemoryInfo getMemoryInfo() {
        ActivityManager activityManager = (ActivityManager) this.getSystemService(ACTIVITY_SERVICE);
        ActivityManager.MemoryInfo memoryInfo = new ActivityManager.MemoryInfo();
        activityManager.getMemoryInfo(memoryInfo);
        return memoryInfo;
    }


}

日志猫

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.dueaoinfo.dueao_job/com.dueaoinfo.dueao_job.MainActivity}: java.lang.NullPointerException: Attempt to get length of null array
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2946)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3081)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1831)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:201)
        at android.app.ActivityThread.main(ActivityThread.java:6823)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:547)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:873)
     Caused by: java.lang.NullPointerException: Attempt to get length of null array
        at com.dueaoinfo.dueao_job.MainActivity.getImageFiles(MainActivity.java:91)
        at com.dueaoinfo.dueao_job.MainActivity.onCreate(MainActivity.java:43)
        at android.app.Activity.performCreate(Activity.java:7224)
        at android.app.Activity.performCreate(Activity.java:7213)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1272)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2926)

Answer 1

您的代码:

list = getImageFiles(Environment.getExternalStorageDirectory());

可以替换为:

  list = getImageFiles(Environment.getExternalStorageDirectory(),"/storage/emulated/0/due/image/");

使其指向您想要选取的文件夹。

引用文献:Environment.getExternalStorageDirectory()

希望这有帮助。