在网格开头从左侧添加 GridView 项目 (android)

Question

我想创建一个类似于 Instagram 的带有图库的应用程序，其中将照片添加到图库会创建一个缩略图，该缩略图出现在 GridView 的开头，而不是结尾。

这是我的代码。

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#f0f0f0">

    <LinearLayout
        android:orientation="vertical"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <Button
            android:id="@+id/bUploadImage"
            android:text="Upload Image"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />
        <GridView xmlns:android="http://schemas.android.com/apk/res/android"
            android:id="@+id/gridview"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:columnWidth="90dp"
            android:numColumns="3"
            android:verticalSpacing="1dp"
            android:horizontalSpacing="3dp"
            android:stretchMode="columnWidth"
            android:gravity="center"
            android:rotationY="180"
            />
    </LinearLayout>

</RelativeLayout>

图像适配器

public class ImageAdapter extends ArrayAdapter {
    private Context mContext;
    private ArrayList<Image> items;

    public ImageAdapter(Context context, int textViewResourceId, ArrayList<Image> items) {
        super(context, textViewResourceId, items);
        this.mContext = context;
        this.items = items;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        notifyDataSetChanged();
        ImageView imageView;
        if (convertView == null) {
            imageView = new ImageView(mContext);
            imageView.setLayoutParams(new GridView.LayoutParams(480, 500));
            imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
            imageView.setPadding(1, 1, 1, 1);
        } else {
            imageView = (ImageView) convertView;
        }
        imageView.setImageBitmap((items.get(position)).getBitmap());
        return imageView;
    }

    public void notifyDatasetChanged(ArrayList<Image> items) {
        this.items = items;
    }

}

主要活动

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    private static final int RESULT_LOAD_IMAGE = 1;
    private ImageAdapter adapter;
    private ArrayList<Image> items = new ArrayList<Image>();

    Button bUploadImage;


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

        bUploadImage = (Button)findViewById(R.id.bUploadImage);
        bUploadImage.setOnClickListener(this);

        GridView gridview = (GridView) findViewById(R.id.gridview);
        adapter = new ImageAdapter(this,0,items);
        gridview.setAdapter(adapter);

    }

    @Override
    public void onClick(View v) {
        switch(v.getId()){
            case R.id.bUploadImage:
                Intent galleryIntent = new Intent(Intent.ACTION_PICK, MediaStore.Images.Media.EXTERNAL_CONTENT_URI);
                startActivityForResult(galleryIntent, RESULT_LOAD_IMAGE);
                break;

        }
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if (requestCode == RESULT_LOAD_IMAGE && resultCode == RESULT_OK && data != null){
            Uri selectedImage = data.getData();
            try {
                Bitmap bitmap = MediaStore.Images.Media.getBitmap(this.getContentResolver(), selectedImage);
                Image i = new Image();
                i.setBitmap(bitmap);
                items.add(i);
            } catch(Exception e){
                e.printStackTrace();
                Toast.makeText(this, e.getMessage(), Toast.LENGTH_SHORT).show();
            }
            adapter.notifyDatasetChanged(items);

        }
    }
}

Answer 1

尝试指定它应该去的位置

list.add(0, yourObject);

将当前位于该位置的元素（如果有）和任何后续元素向右移动。

Answer 2

请注意，您的 notifyDatasetChanged 实际上没有通知任何内容。它只是改变了对数组的引用，但 ArrayAdapter 的内部列表没有改变。你只需要调用 adapter.add(bitmap) 它会自己触发 notifyDatasetChanged 。所有工作都已在 ArrayAdapter 实现中完成。

要解决您的问题，请将您的适配器更改为如下所示：

public class ImageAdapter extends ArrayAdapter<Bitmap> {
    public ImageAdapter(Context context, int textViewResourceId, ArrayList<Bitmap> items) {
        super(context, textViewResourceId, items);
        Bitmap bm = BitmapFactory.decodeResource(context.getResources(),
                android.R.drawable.btn_plus);
        //set btn_plus as first element  in array
        insert(bm, 0);
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ImageView imageView;
        if (convertView == null) {
            imageView = new ImageView(getContext());
            imageView.setLayoutParams(new GridView.LayoutParams(480, 500));
            imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
            imageView.setPadding(1, 1, 1, 1);
        } else {
            imageView = (ImageView) convertView;
        }

        imageView.setImageBitmap(getItem(position));
        return imageView;
    }
}

还要跟踪您需要订阅 setOnItemClickListener 而不是 setOnClickListener 的 GridView 项目的点击事件：

gridview.setOnItemClickListener(new AdapterView.OnItemClickListener() {
    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
       if (position == 0) {
           Intent galleryIntent = new Intent(Intent.ACTION_PICK, MediaStore.Images.Media.EXTERNAL_CONTENT_URI);
           startActivityForResult(galleryIntent, RESULT_LOAD_IMAGE);
           return;
       }

       //Handle click on image
    }
});

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