如何在Android中使用TextWatcher类？

Question

谁能告诉我如何屏蔽 EditText 中的 子字符串 或如何更改 EditText 子字符串输入为密码类型 或替换为另一个字符，例如 123xxxxxxxxx3455

 String contents = et1.getText().toString();
 et1.setText(contents.replace.substring(0, contents.length()-2),"*");

请告诉我如何在 Android 中使用 TextWatcher 方法。

Answer 1

对于 TextWatcher 的使用...

et1.addTextChangedListener(new TextWatcher() {
    @Override
    public void onTextChanged(CharSequence s, int start, int before, int count) {

        // TODO Auto-generated method stub
    }

    @Override
    public void beforeTextChanged(CharSequence s, int start, int count, int after) {

        // TODO Auto-generated method stub
    }

    @Override
    public void afterTextChanged(Editable s) {

        // TODO Auto-generated method stub
    }
});

Answer 2

TextWatcher 接口有 3 个回调方法，当文本发生更改时，这些方法都会按以下顺序调用：

beforeTextChanged(CharSequence s, int start, int count, int after)

• 在将更改应用到文本之前调用。
  s 参数是应用任何更改之前的文本。
  start 参数是文本中更改部分开始的位置。
  count 参数是自 start 位置以来 s 序列中已更改部分的长度。
  after 参数是新序列的长度，它将替换 s 序列中从 start 开始的部分到开始+计数。
  您不得更改从此方法中TextView中的文本（通过使用myTextView.setText(String newText)）。

onTextChanged(CharSequence s, int start, int before, int count)`

• 与 beforeTextChanged 方法类似，但在文本更改之后调用。
  s 参数是应用更改后的文本。
  start 参数与 beforeTextChanged 方法中的参数相同。
  count 参数是 beforeTextChanged 方法中的 after 参数。
  而before参数就是beforeTextChanged方法中的count参数。
  您不得更改从此方法中TextView中的文本（通过使用myTextView.setText(String newText)）。

afterTextChanged(Editable s)

• 您可以通过此方法更改 TextView 中的文本。
  /!\ 警告： 当您更改 TextView 中的文本时，TextWatcher 将再次触发，从而开始无限循环。然后，您应该添加一个 boolean _ignore 属性来防止无限循环。
  示例：

new TextWatcher() {
        boolean _ignore = false; // indicates if the change was made by the TextWatcher itself.

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

            _ignore = true; // prevent infinite loop
            // Change your text here.
            // myTextView.setText(myNewText);
            _ignore = false; // release, so the TextWatcher start to listen again.
        }

        // Other methods...
}

摘要：

---

一个随时可用的类：TextViewListener

就我个人而言，我制作了自定义文本侦听器，它为我提供了单独字符串中的 4 个部分，对我来说，使用起来更加直观。

 /**
   * Text view listener which splits the update text event in four parts:
   * <ul>
   *     <li>The text placed <b>before</b> the updated part.</li>
   *     <li>The <b>old</b> text in the updated part.</li>
   *     <li>The <b>new</b> text in the updated part.</li>
   *     <li>The text placed <b>after</b> the updated part.</li>
   * </ul>
   * Created by Jeremy B.
   */
  
  public abstract class TextViewListener implements TextWatcher {
    /**
     * Unchanged sequence which is placed before the updated sequence.
     */
    private String _before;
  
    /**
     * Updated sequence before the update.
     */
    private String _old;
  
    /**
     * Updated sequence after the update.
     */
    private String _new;
  
    /**
     * Unchanged sequence which is placed after the updated sequence.
     */
    private String _after;
  
    /**
     * Indicates when changes are made from within the listener, should be omitted.
     */
    private boolean _ignore = false;
  
    @Override
    public void beforeTextChanged(CharSequence sequence, int start, int count, int after) {
        _before = sequence.subSequence(0,start).toString();
        _old = sequence.subSequence(start, start+count).toString();
        _after = sequence.subSequence(start+count, sequence.length()).toString();
    }
  
    @Override
    public void onTextChanged(CharSequence sequence, int start, int before, int count) {
        _new = sequence.subSequence(start, start+count).toString();
    }
  
    @Override
    public void afterTextChanged(Editable sequence) {
        if (_ignore)
            return;
  
        onTextChanged(_before, _old, _new, _after);
    }
  
    /**
     * Triggered method when the text in the text view has changed.
     * <br/>
     * You can apply changes to the text view from this method
     * with the condition to call {@link #startUpdates()} before any update,
     * and to call {@link #endUpdates()} after them.
     *
     * @param before Unchanged part of the text placed before the updated part.
     * @param old Old updated part of the text.
     * @param aNew New updated part of the text?
     * @param after Unchanged part of the text placed after the updated part.
     */
    protected abstract void onTextChanged(String before, String old, String aNew, String after);
  
    /**
     * Call this method when you start to update the text view, so it stops listening to it and then prevent an infinite loop.
     * @see #endUpdates()
     */
    protected void startUpdates(){
        _ignore = true;
    }
  
    /**
     * Call this method when you finished to update the text view in order to restart to listen to it.
     * @see #startUpdates()
     */
    protected void endUpdates(){
        _ignore = false;
    }
  }

例子：

myEditText.addTextChangedListener(new TextViewListener() {
        @Override
        protected void onTextChanged(String before, String old, String aNew, String after) {
           // intuitive use of parameters
           String completeOldText = before + old + after;
           String completeNewText = before + aNew + after;
           
           // update TextView
            startUpdates(); // to prevent infinite loop.
            myEditText.setText(myNewText);
            endUpdates();
        }
}

Answer 3

补充答案

这是对其他答案的视觉补充。我对代码和解释的更完整的回答是这里。

• 红色：即将删除（替换）的文本
• 绿色：刚刚添加的文本（替换旧的红色文本）

< img src="https://i.sstatic.net/yhv4A.gif" alt="在此处输入图像描述">

Answer 4

对于 Kotlin 使用 KTX 扩展 函数：
（它使用 TextWatcher 作为之前的答案）

yourEditText.doOnTextChanged { text, start, count, after -> 
        // action which will be invoked when the text is changing
    }

导入 core-KTX：

implementation "androidx.core:core-ktx:1.2.0"

Answer 5

解决方案的更大视角：

@Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.yourlayout, container, false);
        View tv = v.findViewById(R.id.et1);
        ((TextView) tv).addTextChangedListener(new TextWatcher() {
            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
                 SpannableString contentText = new SpannableString(((TextView) tv).getText());
                 String contents = Html.toHtml(contentText).toString();
            }

            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {

                // TODO Auto-generated method stub
            }

            @Override
            public void afterTextChanged(Editable s) {

                // TODO Auto-generated method stub
            }
        });
        return v;
    }

这对我有用，我第一次这样做。

Answer 6

在 Android 中使用 TextWatcher

以下是示例代码。尝试使用 TextView 的 addTextChangedListener 方法

addTextChangedListener(new TextWatcher() {

        BigDecimal previousValue;
        BigDecimal currentValue;

        @Override
        public void onTextChanged(CharSequence s, int start, int before, int
                count) {
            if (isFirstTimeChange) {
                return;
            }
            if (s.toString().length() > 0) {
                try {
                    currentValue = new BigDecimal(s.toString().replace(".", "").replace(',', '.'));
                } catch (Exception e) {
                    currentValue = new BigDecimal(0);
                }
            }
        }

        @Override
        public void beforeTextChanged(CharSequence s, int start, int count,
                int after) {
            if (isFirstTimeChange) {
                return;
            }
            if (s.toString().length() > 0) {
                try {
                    previousValue = new BigDecimal(s.toString().replace(".", "").replace(',', '.'));
                } catch (Exception e) {
                    previousValue = new BigDecimal(0);
                }
            }
        }

        @Override
        public void afterTextChanged(Editable editable) {
            if (isFirstTimeChange) {
                isFirstTimeChange = false;
                return;
            }
            if (currentValue != null && previousValue != null) {
                if ((currentValue.compareTo(previousValue) > 0)) {
                    //setBackgroundResource(R.color.devises_overview_color_green);
                    setBackgroundColor(flashOnColor);
                } else if ((currentValue.compareTo(previousValue) < 0)) {
                    //setBackgroundResource(R.color.devises_overview_color_red);

                    setBackgroundColor(flashOffColor);
                } else {
                    //setBackgroundColor(textColor);
                }
                handler.removeCallbacks(runnable);
                handler.postDelayed(runnable, 1000);
            }
        }
    });

Answer 7

创建自定义 TextWatcher 子类：

public class CustomWatcher implements TextWatcher {

    private boolean mWasEdited = false;

    @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 (mWasEdited){

            mWasEdited = false;
            return;
        }

        // get entered value (if required)
        String enteredValue  = s.toString();

        String newValue = "new value";

        // don't get trap into infinite loop
        mWasEdited = true;
        // just replace entered value with whatever you want
        s.replace(0, s.length(), newValue);

    }
}

为您的 EditText 设置侦听器：

mTargetEditText.addTextChangedListener(new CustomWatcher());

Answer 8

    public class Test extends AppCompatActivity {

    EditText firstEditText;
    EditText secondEditText;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.test);
        firstEditText = (EditText)findViewById(R.id.firstEditText);
        secondEditText = (EditText)findViewById(R.id.secondEditText);

        firstEditText.addTextChangedListener(new EditTextListener());

    }

    private class EditTextListener implements 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) {
            secondEditText.setText(firstEditText.getText());
        }

        @Override
        public void afterTextChanged(Editable s) {
        }
    }
}

Answer 9

如果你用对话框edittext来实现。像这样使用：与其他编辑文本的使用相同。

dialog.getInputEditText().addTextChangedListener(new TextWatcher() {
    @Override
    public void beforeTextChanged(CharSequence charSequence, int start, int before, int count) {
    }

    @Override
    public void onTextChanged(CharSequence charSequence, int start, int before, int count) {
        if (start<2){
                dialog.getActionButton(DialogAction.POSITIVE).setEnabled(false);
            }else{
                double size =  Double.parseDouble(charSequence.toString());
                if (size > 0.000001 && size < 0.999999){
                    dialog.getActionButton(DialogAction.POSITIVE).setEnabled(true);
                }else{
                    ToastHelper.show(HistoryActivity.this, "Size must between 0.1 - 0.9");
                    dialog.getActionButton(DialogAction.POSITIVE).setEnabled(false);
                }

            }
    }

    @Override
    public void afterTextChanged(Editable editable) {

    }
});

Answer 10

我不想实现 TextWatcher 的所有方法，因为我创建了一个抽象类 TextObserver ，问题就解决了：

package com.mindef.idttpda.shared;

// dependencies
import android.text.Editable;
import android.text.TextWatcher;

/**
 * text watcher is converted to abstract class because
 * then not all methods have to be overridden.
 */
public abstract class TextObserver implements TextWatcher {
    public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {}
    public void afterTextChanged(Editable editable) {}
    public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {}
}

Answer 11

我不想重写/实现 TextWatcher 的所有方法，并将 stub 代码放入我不使用的方法中，以便让事情变得简单:-) 我创建了一个抽象类 TextObserver ，瞧，问题解决了。

不知道为什么他们将其实现为接口而不是接口
抽象类，因为大多数时候只使用一种方法
接口是一个契约，规定所有方法都必须是
已实施。

package com.mindef.idttpda.shared;

// dependencies
import android.text.Editable;
import android.text.TextWatcher;

/**
 * text watcher is converted to abstract class because
 * then not all methods have to be overridden.
 */
public abstract class TextObserver implements TextWatcher {
    public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {}
    public void afterTextChanged(Editable editable) {}
    public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {}
}