How to databind to onTextChanged for an EditText on Android?

问题

In Yigit Boyar and George Mount's talk on Android Databinding they illustrate how easy it is to bind to TextWatcher's onTextChanged (at 13:41). On a Button. Are their slides wrong? First of all the Button View doesn't have an onTextChanged property. It neither has a setOnTextChanged method. Neither does EditText. But they both have addTextChangedListener which takes a TextWatcher as input.

So what are they talking about? How do they do it? Their example code does not compile, but gives this error:

Error:(17) No resource identifier found for attribute 'onTextChanged' in package 'android'

How do I bind to a "Text Changed Event" on any View, or EditText in particular, with the Android Databinding framework?

回答1:

Actually it works out of the box. I think my mistake was using an old version of the data binding framework. Using the latest, this is the procedure:

View:

<EditText
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/username"
    android:text="Enter username:"
    android:onTextChanged="@{data.onTextChanged}" />

Model:

public void onTextChanged(CharSequence s, int start, int before, int count) {
    Log.w("tag", "onTextChanged " + s);
}

Make sure you are referncing gradle build tools v1.5.0 or higher and have enabled databinding with android.dataBinding.enabled true in your build.gradle.

edit: Functioning demo project here. view. model.

回答2:

To extend @Nilzors answer, it is also possible to pass text and/or other parameters in the layout:

View:

<EditText
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/username"
    android:text="Enter username:"
    android:onTextChanged="@{(text, start, before, count) -> viewModel.onUsernameTextChanged(text)}" />

ViewModel:

public void onUsernameTextChanged(CharSequence text) {
    // TODO do something with text
}

You always need to pass either zero or all parameters.

回答3:

The Easy Way

If you are using onTextChange() to have updated text in model then you can directly use Two-way Binding.

<data>
    <variable
        name="user"
        type="com.package.User"/>
</data>

<EditText
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@={user.name}"/>

And you model class will have getter & setter.

public class User {
    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

Now the Name in Model will be changed realtime with user interaction. So whenever use binding.getUser().getName(), you will get latest text.

One-Way Binding will only gets updated when model value is changed. It does not update model back real time.

android:text="@{user.name}"

Two-Way Binding update model variable in real time with user input.

android:text="@={user.name}"

The ONLY difference is of = (equal sign) receives data changes to the property and listen to user updates at the same time.

回答4:

the best way for this is adding bind adapter and a text watcher.

public class Model{
    private TextWatcher textWatcher;

public Model(){
        this.textWatcher= getTextWatcherIns();
}

private TextWatcher getTextWatcherIns() {
        return new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {
                //do some thing
            }

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
                //do some thing

            }

            @Override
            public void afterTextChanged(Editable s) {
                //do some thing
            }
        };
    }

    public TextWatcher getTextWatcher() {
        return textWatcher;
    }

    public void setTextWatcher(TextWatcher textWatcher) {
        this.textWatcher = textWatcher;
    }

    @BindingAdapter("textChangedListener")
    public static void bindTextWatcher(EditText editText, TextWatcher textWatcher) {
        editText.addTextChangedListener(textWatcher);
    }
}

and in your xml add this attr to your edit text

<EditText
            android:id="@+id/et"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:textChangedListener="@{model.textWatcher}" />

回答5:

create a class (I named him BindingAdapters). Then define your bindingAdapter methods.

@BindingAdapter("app:textChangedListener")
fun onTextChanged(et: EditText, number: Int) {
et.addTextChangedListener(object : TextWatcher {
    override fun onTextChanged(s: CharSequence, start: Int, before: Int, count: Int) {
        if (et.text.toString().trim().length >= number) {
            et.setBackgroundColor(Color.GREEN)
        }
    }

    override fun beforeTextChanged(s: CharSequence, start: Int, count: Int, after: Int) {}
    override fun afterTextChanged(s: Editable) {}
})

}

set this attr for editText in xml layout

<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
app:textChangedListener="@{3}" />

回答6:

Attach an setOnFocusChangeListener to the EditText, and use compare the textual content with a global variable (of the previous state/content of the field) to determine whether it has changed:

    mEditTextTitle.setOnFocusChangeListener(new View.OnFocusChangeListener() {
        @Override
        public void onFocusChange(View v, boolean hasFocus) {
            if(!hasFocus)
                // check if text has changed       
        }
    });

来源：https://stackoverflow.com/questions/33798426/how-to-databind-to-ontextchanged-for-an-edittext-on-android

标签

android

android-databinding