Summary: Nested Classes | Inherited Constants | Methods | Inherited Methods

PrecomputedTextCompat

Kotlin |Java

public class PrecomputedTextCompat
extends Object implements Spannable

java.lang.Object
↳	androidx.core.text.PrecomputedTextCompat

---

A text which has the character metrics data. A text object that contains the character metrics data and can be used to improve the performance of text layout operations. When a PrecomputedTextCompat is created with a given CharSequence, it will measure the text metrics during the creation. This PrecomputedText instance can be set on TextView or StaticLayout. Since the text layout information will be included in this instance, TextView or StaticLayout will not have to recalculate this information. On API 29 or later, there is full PrecomputedText support by framework. From API 21 to API 27, PrecomputedTextCompat relies on internal text layout cache. PrecomputedTextCompat immediately computes the text layout in the constuctor to warm up the internal text layout cache. On API 20 or before, PrecomputedTextCompat does nothing. Note that any NoCopySpan attached to the original text won't be passed to PrecomputedText.

Summary

Nested classes
class	PrecomputedTextCompat.Params The information required for building PrecomputedTextCompat.

Inherited constants
From interface android.text.Spanned int SPAN_COMPOSING int SPAN_EXCLUSIVE_EXCLUSIVE int SPAN_EXCLUSIVE_INCLUSIVE int SPAN_INCLUSIVE_EXCLUSIVE int SPAN_INCLUSIVE_INCLUSIVE int SPAN_INTERMEDIATE int SPAN_MARK_MARK int SPAN_MARK_POINT int SPAN_PARAGRAPH int SPAN_POINT_MARK int SPAN_POINT_MARK_MASK int SPAN_POINT_POINT int SPAN_PRIORITY int SPAN_PRIORITY_SHIFT int SPAN_USER int SPAN_USER_SHIFT

Public methods
char	charAt(int index)
static PrecomputedTextCompat	create(CharSequence text, PrecomputedTextCompat.Params params) Create a new PrecomputedText which will pre-compute text measurement and glyph positioning information.
int	getParagraphCount() Returns the count of paragraphs.
int	getParagraphEnd(int paraIndex) Returns the paragraph end offset of the text.
int	getParagraphStart(int paraIndex) Returns the paragraph start offset of the text.
PrecomputedTextCompat.Params	getParams() Returns the parameters used to measure this text.
int	getSpanEnd(Object tag)
int	getSpanFlags(Object tag)
int	getSpanStart(Object tag)
<T> T[]	getSpans(int start, int end, Class<T> type)
static Future<PrecomputedTextCompat>	getTextFuture(CharSequence charSequence, PrecomputedTextCompat.Params params, Executor executor) Helper for PrecomputedText that returns a future to be used with AppCompatTextView.setTextFuture(Future).
int	length()
int	nextSpanTransition(int start, int limit, Class type)
void	removeSpan(Object what)
void	setSpan(Object what, int start, int end, int flags)
CharSequence	subSequence(int start, int end)
String	toString()

Inherited methods
From class java.lang.Object Object clone() boolean equals(Object arg0) void finalize() final Class<?> getClass() int hashCode() final void notify() final void notifyAll() String toString() final void wait(long arg0, int arg1) final void wait(long arg0) final void wait()
From interface android.text.Spannable abstract void removeSpan(Object arg0) abstract void setSpan(Object arg0, int arg1, int arg2, int arg3)
From interface android.text.Spanned abstract int getSpanEnd(Object arg0) abstract int getSpanFlags(Object arg0) abstract int getSpanStart(Object arg0) abstract <T> T[] getSpans(int arg0, int arg1, Class<T> arg2) abstract int nextSpanTransition(int arg0, int arg1, Class arg2)
From interface java.lang.CharSequence abstract char charAt(int arg0) default IntStream chars() default IntStream codePoints() abstract int length() abstract CharSequence subSequence(int arg0, int arg1) abstract String toString()

Public methods

charAt

public char charAt (int index)

Parameters
index	int

Returns
char

create

public static PrecomputedTextCompat create (CharSequence text, 
                PrecomputedTextCompat.Params params)

Create a new PrecomputedText which will pre-compute text measurement and glyph positioning information.

This can be expensive, so computing this on a background thread before your text will be presented can save work on the UI thread.

Note that any NoCopySpan attached to the text won't be passed to the created PrecomputedText.

Parameters
text	CharSequence: the text to be measured
params	PrecomputedTextCompat.Params: parameters that define how text will be precomputed

Returns
PrecomputedTextCompat	A PrecomputedText

getParagraphCount

public int getParagraphCount ()

Returns the count of paragraphs.

Returns
int

getParagraphEnd

public int getParagraphEnd (int paraIndex)

Returns the paragraph end offset of the text.

Parameters
paraIndex	int

Returns
int

getParagraphStart

public int getParagraphStart (int paraIndex)

Returns the paragraph start offset of the text.

Parameters
paraIndex	int

Returns
int

getParams

public PrecomputedTextCompat.Params getParams ()

Returns the parameters used to measure this text.

Returns
PrecomputedTextCompat.Params

getSpanEnd

public int getSpanEnd (Object tag)

Parameters
tag	Object

Returns
int

getSpanFlags

public int getSpanFlags (Object tag)

Parameters
tag	Object

Returns
int

getSpanStart

public int getSpanStart (Object tag)

Parameters
tag	Object

Returns
int

getSpans

public T[] getSpans (int start, 
                int end, 
                Class<T> type)

Parameters
start	int
end	int
type	Class

Returns
T[]

getTextFuture

public static Future<PrecomputedTextCompat> getTextFuture (CharSequence charSequence, 
                PrecomputedTextCompat.Params params, 
                Executor executor)

Helper for PrecomputedText that returns a future to be used with AppCompatTextView.setTextFuture(Future). PrecomputedText is suited to compute on a background thread, but when TextView properties are dynamic, it's common to configure text properties and text at the same time, when binding a View. For example, in a RecyclerView Adapter:

     void onBindViewHolder(ViewHolder vh, int position) {
         ItemData data = getData(position);

         vh.textView.setTextSize(...);
         vh.textView.setFontVariationSettings(...);
         vh.textView.setText(data.text);
     }
 

In such cases, using PrecomputedText is difficult, since it isn't safe to defer the setText() code arbitrarily - a layout pass may happen before computation finishes, and will be incorrect if the text isn't ready yet.

With getTextFuture(), you can block on the result of the precomputation safely before the result is needed. AppCompatTextView provides AppCompatTextView.setTextFuture(Future) for exactly this use case. With the following code, the app's layout work is largely done on a background thread:

     void onBindViewHolder(ViewHolder vh, int position) {
         ItemData data = getData(position);

         vh.textView.setTextSize(...);
         vh.textView.setFontVariationSettings(...);

         // start precompute
         Future future = PrecomputedTextCompat.getTextFuture(
                 data.text, vh.textView.getTextMetricsParamsCompat(), myExecutor);

         // and pass future to TextView, which awaits result before measuring
         vh.textView.setTextFuture(future);
     }
 

Because RecyclerView prefetches bind multiple frames in advance while scrolling, the text work generally has plenty of time to complete before measurement occurs.

Note: all TextView layout properties must be set before creating the Params object. If they are changed during the precomputation, this can cause a IllegalArgumentException when the precomputed value is consumed during measure, and doesn't reflect the TextView's current state.

Parameters
charSequence	CharSequence: the text to be displayed
params	PrecomputedTextCompat.Params: the parameters to be used for displaying text
executor	Executor: the executor to be process the text layout. If null is passed, the default single threaded pool will be used.

Returns
Future<PrecomputedTextCompat>	a future of the precomputed text

See also:

• AppCompatTextView.setTextFuture(Future)

length

public int length ()

Returns
int

nextSpanTransition

public int nextSpanTransition (int start, 
                int limit, 
                Class type)

Parameters
start	int
limit	int
type	Class

Returns
int

removeSpan

public void removeSpan (Object what)

Parameters
what	Object

Throws
IllegalArgumentException	if MetricAffectingSpan is specified.

setSpan

public void setSpan (Object what, 
                int start, 
                int end, 
                int flags)

Parameters
what	Object
start	int
end	int
flags	int

Throws
IllegalArgumentException	if MetricAffectingSpan is specified.

subSequence

public CharSequence subSequence (int start, 
                int end)

Parameters
start	int
end	int

Returns
CharSequence

toString

public String toString ()

Returns
String