How to add properly UiHandler for BlurEvent in GWT?

问题

Normally if we have some textField in GWT we can add a BlurHandler by the following code:

textField.addBlurHandler(new BlurHandler() {
        @Override
        public void onBlur(BlurEvent event) {
             //what we need    
        }
    });

But if we use UiBinder and our textField is annotated by @UiField and it is mentioned in our ui.xml file we can add BlurHandler by this code as well:

@UiHandler("textField")
protected void createBlurHandler(BlurEvent event) {

}

I guess I am right here because it works like this. So, the question is, can we actually define BlurHandler inside ui.xml file?

For example, it is possible to add inputMaxLength and some other attributes there, does GWT has some possibility like onChange method or are these ways that I described the only possibilities?

I would like to have something like this:

<g:TextBox ui:field="textField" onBlur="methodName" />

Is it possible?

回答1:

I am pretty sure what you are asking is not possible. The problem is that you wouldn't be able to use reflection to figure out which method you want to call. However you can extends the TextBox class and use that inside your template. The extended class could have it's own properties that can be set in the template. An example is as follows where I set the default test on my own DefaultTextBox.

public class DefaultTextBox extends TextBox {

    /**
     * The text color used when the box is disabled and empty.
     */
    private static final String TEXTBOX_DISABLED_COLOR = "#AAAAAA";

    private final String defaultText;

    public @UiConstructor
    DefaultTextBox(final String defaultText) {
        this.defaultText = defaultText;
        resetDefaultText();

        // Add focus and blur handlers.
        addFocusHandler(new FocusHandler() {
            @Override
            public void onFocus(FocusEvent event) {
                getElement().getStyle().clearColor();
                getElement().getStyle().clearFontStyle();
                if (defaultText.equals(getText())) {
                    setText("");
                }
            }
        });

        addBlurHandler(new BlurHandler() {
            @Override
            public void onBlur(BlurEvent event) {
                if ("".equals(getText())) {
                    resetDefaultText();
                }
            }
        });
    }

    public String getDefaultText() {
        return defaultText;
    }

    @Override
    public void setText(String text) {
        if (text == null) {
            super.setText(getDefaultText());
        } else {
            getElement().getStyle().clearColor();
            getElement().getStyle().clearFontStyle();
            super.setText(text);
        }
    }

    public String getText() {

        return super.getText();
    }

    /**
     * This is override so that the editor framework will not get the default
     * value but the actual null value when the default text is in the box.
     */
    @Override
    public String getValue() {
        try {
            return getValueOrThrow();
        } catch (ParseException e) {
            return null;
        }

    }

    @Override
    public void setValue(String value) {
        setText(value);
    }

    /**
     * This is overridden from the parent class because this is 
     * how the editor gets the value.
     */
    public String getValueOrThrow() throws ParseException {
        if (defaultText.equals(super.getValueOrThrow())) {
            return null;
        }
        return super.getValueOrThrow();
    }


    /**
     * Reset the text box to the default text.
     */
    public void resetDefaultText() {
        setText(defaultText);
        getElement().getStyle().setColor(TEXTBOX_DISABLED_COLOR);
        getElement().getStyle().setFontStyle(FontStyle.ITALIC);
    }
}

Then in the template you can set properties like this.

<w:DefaultTextBox defaultText="name" ui:field="nameTextBox" />

This will also work with setters, you can set properties without having to use the @UiConstructor but in my case I wanted to make sure that there was no empty constructor for this class.

来源：https://stackoverflow.com/questions/26480214/how-to-add-properly-uihandler-for-blurevent-in-gwt

标签

java

gwt

uibinder