CODEWITHSUNDEEP
androidandroid-edittexttextview
Suragch
Suragch

Reputation: 511558

How does an Android EditText (TextView) draw the blinking cursor?

I'm making my own Mongolian vertical script TextView (and EditText) from scratch by extending View. I'm trying to understand how the blinking cursor is implemented in the Android TextView source code. It seems to be handled by an mEditor instance of the Editor class. In that class I found a drawCursor method:

private void drawCursor(Canvas canvas, int cursorOffsetVertical) {
    final boolean translate = cursorOffsetVertical != 0;
    if (translate) canvas.translate(0, cursorOffsetVertical);
    for (int i = 0; i < mCursorCount; i++) {
        mCursorDrawable[i].draw(canvas);
    }
    if (translate) canvas.translate(0, -cursorOffsetVertical);
}

Apparently, the cursor itself is a Drawable of some type.

So I am finding pieces, but I can't see the forest through the trees. Could someone who understands this better than me tell me in plain English how the blinking cursor works?

Here are some specific points I don't really understand:

Note:

The accepted answer answers my question as I asked it. However, I would be glad to accept a different answer if anyone can add a more canonical one that explains things in more detail.

Upvotes: 9

Views: 2413

Answers (2)

Fatehali Asamadi
Fatehali Asamadi

Reputation: 226

You can find this method in the TextView class:

public void setCursorVisible(boolean visible) {

    if (visible && mEditor == null) return; // visible is the default value with no edit data
    createEditorIfNeeded();
    if (mEditor.mCursorVisible != visible) {
        mEditor.mCursorVisible = visible;
        invalidate();

        mEditor.makeBlink();

        // InsertionPointCursorController depends on mCursorVisible
        mEditor.prepareCursorControllers();
    }
}

Upvotes: 2

Nikola Despotoski
Nikola Despotoski

Reputation: 50538

  1. EditText is just editable TextView, Layout is used for measurements, calculation, where and how the text will laid out. Drawable is there just to hold the look of the cursor, later being drawn on the Canvas.
  2. Only cursor Path is invalidated.

Blinking basically is recursive Runnable that a Handler executes every 500ms (guessing), in on-off fashion, and it is rescheduled while EditText has focus. This also can be achieved by looping ValueAnimator of int, where the cursor drawable alpha will be toggled between 0 and 255.

Upvotes: 10

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