What really happens when setText() is called on an EditText?











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This is a part of the code:



editText.setText("Some Text", TextView.BufferType.EDITABLE);

Editable editable = (Editable) editText.getText();

// value of editable.toString() here is "Some Text"

editText.setText("Another Text", TextView.BufferType.EDITABLE);

// value of editable.toString() is still "Some Text"


Why the value of editable.toString() did not change? Thanks










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    up vote
    1
    down vote

    favorite












    This is a part of the code:



    editText.setText("Some Text", TextView.BufferType.EDITABLE);

    Editable editable = (Editable) editText.getText();

    // value of editable.toString() here is "Some Text"

    editText.setText("Another Text", TextView.BufferType.EDITABLE);

    // value of editable.toString() is still "Some Text"


    Why the value of editable.toString() did not change? Thanks










    share|improve this question
























      up vote
      1
      down vote

      favorite









      up vote
      1
      down vote

      favorite











      This is a part of the code:



      editText.setText("Some Text", TextView.BufferType.EDITABLE);

      Editable editable = (Editable) editText.getText();

      // value of editable.toString() here is "Some Text"

      editText.setText("Another Text", TextView.BufferType.EDITABLE);

      // value of editable.toString() is still "Some Text"


      Why the value of editable.toString() did not change? Thanks










      share|improve this question













      This is a part of the code:



      editText.setText("Some Text", TextView.BufferType.EDITABLE);

      Editable editable = (Editable) editText.getText();

      // value of editable.toString() here is "Some Text"

      editText.setText("Another Text", TextView.BufferType.EDITABLE);

      // value of editable.toString() is still "Some Text"


      Why the value of editable.toString() did not change? Thanks







      android android-edittext textview android-editable






      share|improve this question













      share|improve this question











      share|improve this question




      share|improve this question










      asked Nov 13 at 15:33









      H. Riantsoa

      326




      326
























          1 Answer
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          You assigned editText.getText() to a variable. That means its value won't change.



          When you call setText(), the original text is overwritten with the new CharSequence; the original instance of the Editable that getText() returns is no longer part of the TextView, so your editable variable is no longer attached to the TextView.



          Take a look at TextView's getEditableText() (this is what EditText calls from getText()):



          public Editable getEditableText() {
          return (mText instanceof Editable) ? (Editable) mText : null;
          }


          If mText is an Editable Object, then it'll return it. Otherwise, it'll return null.



          setText() eventually makes its way to setTextInternal():



          private void setTextInternal(@Nullable CharSequence text) {
          mText = text;
          mSpannable = (text instanceof Spannable) ? (Spannable) text : null;
          mPrecomputed = (text instanceof PrecomputedText) ? (PrecomputedText) text : null;
          }


          As you can see, it just overwrites the mText field, meaning your Editable instance is no longer the instance that the EditText has.



          TextView.java






          share|improve this answer





















          • I agree with most of this answer, but simply assigning a value to a variable doesn't mean that the value will never change. SpannableStringBuilder implements Editable, and so the results of its toString() method can change over time.
            – Ben P.
            Nov 13 at 15:46










          • @BenP. yes, but OP isn't using a SpannableStringBuilder. OP is using an EditText, which does overwrite the variable returned by getText(). That means that the editable variable OP has won't change when setText() is called.
            – TheWanderer
            Nov 13 at 15:50










          • My point is just that the blanket statement "You assigned X to a variable, therefore X's value won't change" is not true in general. It may be true in this case, but it would be a bad lesson to "learn" for java programming in general.
            – Ben P.
            Nov 13 at 15:53










          • It wasn't meant as a blanket statement.
            – TheWanderer
            Nov 13 at 15:54










          • ` Editable t = mEditableFactory.newEditable(text); text = t; ` also helped me a lot. Thanks
            – H. Riantsoa
            Nov 13 at 16:54











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          1 Answer
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          active

          oldest

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          1 Answer
          1






          active

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          active

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          up vote
          2
          down vote



          accepted










          You assigned editText.getText() to a variable. That means its value won't change.



          When you call setText(), the original text is overwritten with the new CharSequence; the original instance of the Editable that getText() returns is no longer part of the TextView, so your editable variable is no longer attached to the TextView.



          Take a look at TextView's getEditableText() (this is what EditText calls from getText()):



          public Editable getEditableText() {
          return (mText instanceof Editable) ? (Editable) mText : null;
          }


          If mText is an Editable Object, then it'll return it. Otherwise, it'll return null.



          setText() eventually makes its way to setTextInternal():



          private void setTextInternal(@Nullable CharSequence text) {
          mText = text;
          mSpannable = (text instanceof Spannable) ? (Spannable) text : null;
          mPrecomputed = (text instanceof PrecomputedText) ? (PrecomputedText) text : null;
          }


          As you can see, it just overwrites the mText field, meaning your Editable instance is no longer the instance that the EditText has.



          TextView.java






          share|improve this answer





















          • I agree with most of this answer, but simply assigning a value to a variable doesn't mean that the value will never change. SpannableStringBuilder implements Editable, and so the results of its toString() method can change over time.
            – Ben P.
            Nov 13 at 15:46










          • @BenP. yes, but OP isn't using a SpannableStringBuilder. OP is using an EditText, which does overwrite the variable returned by getText(). That means that the editable variable OP has won't change when setText() is called.
            – TheWanderer
            Nov 13 at 15:50










          • My point is just that the blanket statement "You assigned X to a variable, therefore X's value won't change" is not true in general. It may be true in this case, but it would be a bad lesson to "learn" for java programming in general.
            – Ben P.
            Nov 13 at 15:53










          • It wasn't meant as a blanket statement.
            – TheWanderer
            Nov 13 at 15:54










          • ` Editable t = mEditableFactory.newEditable(text); text = t; ` also helped me a lot. Thanks
            – H. Riantsoa
            Nov 13 at 16:54















          up vote
          2
          down vote



          accepted










          You assigned editText.getText() to a variable. That means its value won't change.



          When you call setText(), the original text is overwritten with the new CharSequence; the original instance of the Editable that getText() returns is no longer part of the TextView, so your editable variable is no longer attached to the TextView.



          Take a look at TextView's getEditableText() (this is what EditText calls from getText()):



          public Editable getEditableText() {
          return (mText instanceof Editable) ? (Editable) mText : null;
          }


          If mText is an Editable Object, then it'll return it. Otherwise, it'll return null.



          setText() eventually makes its way to setTextInternal():



          private void setTextInternal(@Nullable CharSequence text) {
          mText = text;
          mSpannable = (text instanceof Spannable) ? (Spannable) text : null;
          mPrecomputed = (text instanceof PrecomputedText) ? (PrecomputedText) text : null;
          }


          As you can see, it just overwrites the mText field, meaning your Editable instance is no longer the instance that the EditText has.



          TextView.java






          share|improve this answer





















          • I agree with most of this answer, but simply assigning a value to a variable doesn't mean that the value will never change. SpannableStringBuilder implements Editable, and so the results of its toString() method can change over time.
            – Ben P.
            Nov 13 at 15:46










          • @BenP. yes, but OP isn't using a SpannableStringBuilder. OP is using an EditText, which does overwrite the variable returned by getText(). That means that the editable variable OP has won't change when setText() is called.
            – TheWanderer
            Nov 13 at 15:50










          • My point is just that the blanket statement "You assigned X to a variable, therefore X's value won't change" is not true in general. It may be true in this case, but it would be a bad lesson to "learn" for java programming in general.
            – Ben P.
            Nov 13 at 15:53










          • It wasn't meant as a blanket statement.
            – TheWanderer
            Nov 13 at 15:54










          • ` Editable t = mEditableFactory.newEditable(text); text = t; ` also helped me a lot. Thanks
            – H. Riantsoa
            Nov 13 at 16:54













          up vote
          2
          down vote



          accepted







          up vote
          2
          down vote



          accepted






          You assigned editText.getText() to a variable. That means its value won't change.



          When you call setText(), the original text is overwritten with the new CharSequence; the original instance of the Editable that getText() returns is no longer part of the TextView, so your editable variable is no longer attached to the TextView.



          Take a look at TextView's getEditableText() (this is what EditText calls from getText()):



          public Editable getEditableText() {
          return (mText instanceof Editable) ? (Editable) mText : null;
          }


          If mText is an Editable Object, then it'll return it. Otherwise, it'll return null.



          setText() eventually makes its way to setTextInternal():



          private void setTextInternal(@Nullable CharSequence text) {
          mText = text;
          mSpannable = (text instanceof Spannable) ? (Spannable) text : null;
          mPrecomputed = (text instanceof PrecomputedText) ? (PrecomputedText) text : null;
          }


          As you can see, it just overwrites the mText field, meaning your Editable instance is no longer the instance that the EditText has.



          TextView.java






          share|improve this answer












          You assigned editText.getText() to a variable. That means its value won't change.



          When you call setText(), the original text is overwritten with the new CharSequence; the original instance of the Editable that getText() returns is no longer part of the TextView, so your editable variable is no longer attached to the TextView.



          Take a look at TextView's getEditableText() (this is what EditText calls from getText()):



          public Editable getEditableText() {
          return (mText instanceof Editable) ? (Editable) mText : null;
          }


          If mText is an Editable Object, then it'll return it. Otherwise, it'll return null.



          setText() eventually makes its way to setTextInternal():



          private void setTextInternal(@Nullable CharSequence text) {
          mText = text;
          mSpannable = (text instanceof Spannable) ? (Spannable) text : null;
          mPrecomputed = (text instanceof PrecomputedText) ? (PrecomputedText) text : null;
          }


          As you can see, it just overwrites the mText field, meaning your Editable instance is no longer the instance that the EditText has.



          TextView.java







          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered Nov 13 at 15:40









          TheWanderer

          5,73611026




          5,73611026












          • I agree with most of this answer, but simply assigning a value to a variable doesn't mean that the value will never change. SpannableStringBuilder implements Editable, and so the results of its toString() method can change over time.
            – Ben P.
            Nov 13 at 15:46










          • @BenP. yes, but OP isn't using a SpannableStringBuilder. OP is using an EditText, which does overwrite the variable returned by getText(). That means that the editable variable OP has won't change when setText() is called.
            – TheWanderer
            Nov 13 at 15:50










          • My point is just that the blanket statement "You assigned X to a variable, therefore X's value won't change" is not true in general. It may be true in this case, but it would be a bad lesson to "learn" for java programming in general.
            – Ben P.
            Nov 13 at 15:53










          • It wasn't meant as a blanket statement.
            – TheWanderer
            Nov 13 at 15:54










          • ` Editable t = mEditableFactory.newEditable(text); text = t; ` also helped me a lot. Thanks
            – H. Riantsoa
            Nov 13 at 16:54


















          • I agree with most of this answer, but simply assigning a value to a variable doesn't mean that the value will never change. SpannableStringBuilder implements Editable, and so the results of its toString() method can change over time.
            – Ben P.
            Nov 13 at 15:46










          • @BenP. yes, but OP isn't using a SpannableStringBuilder. OP is using an EditText, which does overwrite the variable returned by getText(). That means that the editable variable OP has won't change when setText() is called.
            – TheWanderer
            Nov 13 at 15:50










          • My point is just that the blanket statement "You assigned X to a variable, therefore X's value won't change" is not true in general. It may be true in this case, but it would be a bad lesson to "learn" for java programming in general.
            – Ben P.
            Nov 13 at 15:53










          • It wasn't meant as a blanket statement.
            – TheWanderer
            Nov 13 at 15:54










          • ` Editable t = mEditableFactory.newEditable(text); text = t; ` also helped me a lot. Thanks
            – H. Riantsoa
            Nov 13 at 16:54
















          I agree with most of this answer, but simply assigning a value to a variable doesn't mean that the value will never change. SpannableStringBuilder implements Editable, and so the results of its toString() method can change over time.
          – Ben P.
          Nov 13 at 15:46




          I agree with most of this answer, but simply assigning a value to a variable doesn't mean that the value will never change. SpannableStringBuilder implements Editable, and so the results of its toString() method can change over time.
          – Ben P.
          Nov 13 at 15:46












          @BenP. yes, but OP isn't using a SpannableStringBuilder. OP is using an EditText, which does overwrite the variable returned by getText(). That means that the editable variable OP has won't change when setText() is called.
          – TheWanderer
          Nov 13 at 15:50




          @BenP. yes, but OP isn't using a SpannableStringBuilder. OP is using an EditText, which does overwrite the variable returned by getText(). That means that the editable variable OP has won't change when setText() is called.
          – TheWanderer
          Nov 13 at 15:50












          My point is just that the blanket statement "You assigned X to a variable, therefore X's value won't change" is not true in general. It may be true in this case, but it would be a bad lesson to "learn" for java programming in general.
          – Ben P.
          Nov 13 at 15:53




          My point is just that the blanket statement "You assigned X to a variable, therefore X's value won't change" is not true in general. It may be true in this case, but it would be a bad lesson to "learn" for java programming in general.
          – Ben P.
          Nov 13 at 15:53












          It wasn't meant as a blanket statement.
          – TheWanderer
          Nov 13 at 15:54




          It wasn't meant as a blanket statement.
          – TheWanderer
          Nov 13 at 15:54












          ` Editable t = mEditableFactory.newEditable(text); text = t; ` also helped me a lot. Thanks
          – H. Riantsoa
          Nov 13 at 16:54




          ` Editable t = mEditableFactory.newEditable(text); text = t; ` also helped me a lot. Thanks
          – H. Riantsoa
          Nov 13 at 16:54


















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