如何检查 SQL 数据库游标中的列是否为空？

Question

我有数据库，他们可以在其中输入图像作为字段之一。图像保存到 phone，URI 保存到数据库。

当用户决定不为项目放入图像时，我遇到了麻烦。

我正在尝试编写 if/else 语句，其中 "if" 条件检查光标的图像列是否为空。我只是不知道要在 if 条件中输入什么。

这是我正在使用的代码。基本上我想做到这一点，如果光标的 COLUMN_WINE_IMAGE 为空，就干杯。如果不为空，则设置图片。

//This section turns the database's image URI stored in this cursor into a bitmap, and then sets the ImageView.
    Bitmap bitmap = null;
    try {
        if (............){
            Toast.makeText(this, "No image was taken for this item. (TOAST IS JUST TESTING PURPOSES)", Toast.LENGTH_SHORT).show();
        }else{
            bitmap = MediaStore.Images.Media.getBitmap(this.getContentResolver(), Uri.parse(cursor.getString(cursor.getColumnIndexOrThrow(WineContract.WineEntry.COLUMN_WINE_IMAGE))));
            mFullImage.setImageBitmap(bitmap);
        }
    } catch (IOException e) {
        e.printStackTrace();
    }

这是我尝试过但没有成功的其中一件事的示例：

if (Uri.parse(cursor.getString(cursor.getColumnIndexOrThrow(WineContract.WineEntry.COLUMN_WINE_IMAGE))).equals(null)){ 

//This returns error: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.jeremy.sqlwine/com.example.jeremy.sqlwine.DetailsActivity}: java.lang.NullPointerException: uriString

Answer 1

改用这个：

if(cursor.getColumnIndexOrThrow(WineContract.WineEntry.COLUMN_WINE_IMAGE) == null)

更新：

cursor.isNull(cursor.getColumnIndexOrThrow(WineContract.WineEntry.COLUMN_WINE_IMAGE))

Answer 2

在单独的方法中检索列值。然后在使用前检查 return 值。

尝试这样的事情：

private String checkDatabaseValue(Cursor cursor){
    String result = null;
    try{
        //This can throw an error if the column is not found
        int index = cursor.getColumnIndexOrThrow(WineContract.WineEntry.COLUMN_WINE_IMAGE);
        result = cursor.getString(index).trim();
    }
    catch(Exception ex){
        // determine what threw the error and handle appropriately
        Log.e(TAG, ex.getMessage());
    }
    return result;
}

然后在这里使用它：

Bitmap bitmap = null;
    try {
        // I'm assuming you have the cursor from somewhere!!
        String imageFile = checkDatabaseValue(cursor);
        if (imageFile == null){
            Toast.makeText(this, "No image was taken for this item. (TOAST IS JUST TESTING PURPOSES)", Toast.LENGTH_SHORT).show();
            return;
        }

        if(!imageFile.isEmpty()){
            bitmap = MediaStore.Images.Media.getBitmap(this.getContentResolver(), Uri.parse(imageFile));
            mFullImage.setImageBitmap(bitmap);
        else{
            Toast.makeText(this, "Empty String. (TOAST IS JUST TESTING PURPOSES)", Toast.LENGTH_SHORT).show();
        }
    } catch (IOException e) {
        e.printStackTrace();
    }

如何检查 SQL 数据库游标中的列是否为空？

How do I check if a column from a SQL database cursor is empty?

java

android

cursor