从外部存储获取图像并将其显示在图库中

Question

I've created a folder called "TopClothes" and I have some photos there. It is store in my SD Card. I've been looking for an answer but can't seem to find one. I just want to be able to "read" those images in the folder and display them in a Gallery in my app. Is there a way of doing this? Here's some of what I have on my MainActivity :

gal = (Gallery)findViewById(R.id.gallery1);
    gal.setAdapter(new ImageAdapter(this));
    iv = (ImageView)findViewById(R.id.imgView);

File file = new File(Environment.getExternalStorageDirectory()+"/TopClothes/");
    File imageList[] = file.listFiles();

     for(int i=0;i<imageList.length;i++)
     {
       Log.e("Image: "+i+": path", imageList[i].getAbsolutePath());
       Bitmap b = BitmapFactory.decodeFile(imageList[i].getAbsolutePath());
       iv.setImageBitmap(b);
     }

The image is set correctly, but its only 1 image, and I want to have lots of images and be able to scroll and see them.

This is my ArrayAdapter :

private Context context;
public Integer[] ImgIds = {};

public ImageAdapter(Context context) {
    // TODO Auto-generated constructor stub
    this.context = context;
}

@Override
public int getCount() {
    // TODO Auto-generated method stub
    return ImgIds.length;
}

@Override
public Object getItem(int position) {
    // TODO Auto-generated method stub
    return position;
}

@Override
public long getItemId(int position) {
    // TODO Auto-generated method stub
    return position;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    // TODO Auto-generated method stub
    ImageView imgView = null;
    if(convertView == null){
        imgView = new ImageView(context);
        imgView.setLayoutParams(new Gallery.LayoutParams(300, 500));
    }else {
        imgView = (ImageView)convertView;
    }

    File file = new File(Environment.getExternalStorageDirectory()+"/TopClothes/");
    File imageList[] = file.listFiles();

    imgView.setImageResource(ImgIds[position]);
    return imgView;
}

Notice that public Integer[] ImgIds = {}; is empty. Should the file path be there?

Answer 1

There are a few different issues with your current implementation.

1. Storage access should be minimized when possible.

You are opening files in many places, sometimes using the results, sometimes not using the results at all, and sometimes only using a small subset of the results.

In your first code sample, you retrieve the entire contents of the "TopClothes" file, but only place a single image file into the ImageView you have declared. This image will be the last image retrieved from the file.

gal = (Gallery)findViewById(R.id.gallery1);
gal.setAdapter(new ImageAdapter(this));
iv = (ImageView)findViewById(R.id.imgView);

// This File open could be reduced into a single retrieval for the image 
//  which will be used in the ImageView.

File file = new File(Environment.getExternalStorageDirectory()+"/TopClothes/");
File imageList[] = file.listFiles();

// This entire for loop could be removed and replaced with a single Bitmap creation and
//  assignment into the ImageView.

for(int i=0;i<imageList.length;i++)
{
    Log.e("Image: "+i+": path", imageList[i].getAbsolutePath());
    Bitmap b = BitmapFactory.decodeFile(imageList[i].getAbsolutePath());
    iv.setImageBitmap(b);
}

A second problem related to accessing storage is how your Adapter is retrieving data directly from the storage when creating the view to be returned. You should probably retrieve that image data once, and then pass the entire image data list into the adapter for use. As implemented, you are retrieving the entire contents of this "TopClothing" directory for each and every ImageView in the Gallery, then choosing a single image from the data to put into an ImageView.

This is a lot of unnecessary overhead

2. The Adapter does not actually put an image into the views that it returns.

This does not use the results retrieved from storage to create each view.

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    ImageView imgView = null;
    if(convertView == null){
        imgView = new ImageView(context);
        imgView.setLayoutParams(new Gallery.LayoutParams(300, 500));
    }else {
        imgView = (ImageView)convertView;
    }

    File file = new File(Environment.getExternalStorageDirectory()+"/TopClothes/");

    // ImgIds should either be filled with the data when loaded from this directory.
    //  Rather than 'imageList'.
    File imageList[] = file.listFiles();

    // OR This should give the ImageView an image from the 'imageList' which was actually filled.
    imgView.setImageResource(ImgIds[position]);
    return imgView;
}