How can I change the EditText text without trigger

问题:

I have an EditText field with a Customer Text Watcher on it. In a piece of code I need to change the value in the EditText which I do using .setText("whatever").

The problem is as soon as I make that change the afterTextChanged method gets called which created an infinite loop. How can I change the text without it triggering afterTextChanged?

I need the text in the afterTextChanged method so don't suggest removing the TextWatcher.

回答1:

You could unregister the watcher, and then re-register it.

Alternatively, you could set a flag so that your watcher knows when you have just changed the text yourself (and therefore should ignore it).

回答2:

You can check which View currently has the focus to distinguish between user and program triggered events.

EditText myEditText = (EditText) findViewById(R.id.myEditText);

myEditText.addTextChangedListener(new TextWatcher() {

    @Override
    public void onTextChanged(CharSequence s, int start, int before, int count) {
        if (getCurrentFocus() == myEditText) {
            // is only executed if the EditText was directly changed by the user
        }
    }

    //...
});

Edit: As LairdPleng correctly mentioned, this does not work if the myEditText already has the focus and you programmatically change the text. So, before calling myEditText.setText(...) you should call myEditText.clearFocus() as Chack said, which solves this problem as well.

回答3:

Easy trick to fix ... as long a your logic to derive the new edit text value is idempotent (which it probably would be, but just saying). In your listener method, only modify the edit text if the current value is different than the last time you modified the value.

e.g.,

TextWatcher tw = new TextWatcher() {
  private String lastValue = "";

  @Override
  public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {
  }

  @Override
  public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {
  }

  @Override
  public void afterTextChanged(Editable editable) {

    // Return value of getNewValue() must only depend
    // on the input and not previous state
    String newValue = getNewValue(editText.getText().toString());
    if (!newValue.equals(lastValue)) {
      lastValue = newValue;

      editText.setText(newValue);
    }
  }
};

回答4:

public class MyTextWatcher implements TextWatcher {
    private EditText et;

    // Pass the EditText instance to TextWatcher by constructor
    public MyTextWatcher(EditText et) {
        this.et = et;
    }

    @Override
    public void afterTextChanged(Editable s) {
        // Unregister self before update
        et.removeTextChangedListener(this);

        // The trick to update text smoothly.
        s.replace(0, s.length(), "text");

        // Re-register self after update
        et.addTextChangedListener(this);
    }
}

Usage:

et_text.addTextChangedListener(new MyTextWatcher(et_text));

You may feel a little bit lag when entering text rapidly if you are using editText.setText() instead of editable.replace().

回答5:

Hi if you need to stay focused on EditText change text you could request focus. This worked for me:

if (getCurrentFocus() == editText) {
    editText.clearFocus();
    editText.setText("...");
    editText.requestFocus();
}

回答6:

try this logic: I wanted to setText("") without going to infinite loop and this code works for me. I hope you can modify this to fit your requirement

        final EditText text= (EditText)findViewById(R.id.text);
        text.addTextChangedListener(new TextWatcher() {
        @Override
        public void beforeTextChanged(CharSequence s, int start, int count, int after) {
        }
        @Override
        public void onTextChanged(CharSequence s, int start, int before, int count) {

        }
        @Override
        public void afterTextChanged(Editable s) {
            if(s.toString().isEmpty())return;
            text.setText("");
            //your code
        }
    });

回答7:

My variant:

public class CustomEditText extends AppCompatEditText{
    TextWatcher l;

    public CustomEditText(Context context, AttributeSet attrs) {
        super(context, attrs);
    }
    public void setOnTextChangeListener(TextWatcher l) {
        try {
            removeTextChangedListener(this.l);
        } catch (Throwable e) {}
        addTextChangedListener(l);
        this.l = l;
    }

    public void setNewText(CharSequence s) {
        final TextWatcher l = this.l;
        setOnTextChangeListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {

            }

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {

            }

            @Override
            public void afterTextChanged(Editable s) {

            }
        });
        setText(s);
        post(new Runnable() {
            @Override
            public void run() {
                setOnTextChangeListener(l);
            }
        });
    }


}

Set listeners only using setOnTextChangeListener() and set text only using setNewText (I wanted to override setText(), but it is final)

回答8:

I've created an abstract class which mitigates the cyclic issue of when a modification to the EditText is made via a TextWatcher.

/**
 * An extension of TextWatcher which stops further callbacks being called as a result of a change
 * happening within the callbacks themselves.
 */
public abstract class EditableTextWatcher implements TextWatcher {

    private boolean editing;

    @Override
    public final void beforeTextChanged(CharSequence s, int start, int count, int after) {
        if (editing)
            return;

        editing = true;
        try {
            beforeTextChange(s, start, count, after);
        } finally {
            editing = false;
        }
    }

    abstract void beforeTextChange(CharSequence s, int start, int count, int after);

    @Override
    public final void onTextChanged(CharSequence s, int start, int before, int count) {
    if (editing)
        return;

        editing = true;
        try {
            onTextChange(s, start, before, count);
        } finally {
            editing = false;
        }
    }

    abstract void onTextChange(CharSequence s, int start, int before, int count);

    @Override
    public final void afterTextChanged(Editable s) {
        if (editing)
            return;

        editing = true;
        try {
            afterTextChange(s);
        } finally {
            editing = false;
        }
    }    

    public boolean isEditing() {
        return editing;
    }

    abstract void afterTextChange(Editable s);
}

回答9:

Here's a handy class that provides a simpler interface than TextWatcher for the normal case of wanting to see changes as they occur. It also allows for ignoring the next change as the OP requested.

public class EditTexts {
    public final static class EditTextChangeListener implements TextWatcher {
        private final Consumer<String> onEditTextChanged;
        private boolean ignoreNextChange = false;
        public EditTextChangeListener(Consumer<String> onEditTextChanged){
            this.onEditTextChanged = onEditTextChanged;
        }
        public void ignoreNextChange(){
            ignoreNextChange = true;
        }
        @Override public void beforeTextChanged(CharSequence __, int ___, int ____, int _____) { }
        @Override public void onTextChanged(CharSequence __, int ___, int ____, int _____) { }
        @Override public void afterTextChanged(Editable s) {
            if (ignoreNextChange){
                ignoreNextChange = false;
            } else {
                onEditTextChanged.accept(s.toString());
            }
        }
    }
}

Use it like this:

EditTexts.EditTextChangeListener listener = new EditTexts.EditTextChangeListener(s -> doSomethingWithString(s));
editText.addTextChangedListener(listener);

Whenever you want to modify the contents of editText without causing a cascade of recursive edits, do this:

listener.ignoreNextChange();
editText.setText("whatever"); // this won't trigger the listener

回答10:

I use that way:

mEditText.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {}

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {}

            @Override
            public void afterTextChanged(Editable s) {
                if (mEditText.isFocused()) { //<-- check if is focused 
                    mEditText.setTag(true);
                }
            }
        });

And every time you need to change text programatically, first clear the focus

mEditText.clearFocus();
mEditText.setText(lastAddress.complement);

回答11:

You should ensure your implementation of text changes is stable and does not change the text if no change is needed. Normally that would be any content that's already been through the watcher once.

The most common mistake is to set a new text in the associated EditText or the Editable even though the text was not actually changes.

On top of that, if you make your changes to the Editable instead of some specific View, you can easily resuse your watcher, and also you can test it in isolation with some unit tests to ensure it has the outcome you want.

Since Editable is an interface you could even use a dummy implementation of it that throws a RuntimeException if any of its methods are called that try to change its contents, when testing content that should be stable.