PrecomputedTextCompat
open class PrecomputedTextCompat : Spannable
kotlin.Any | |
↳ | 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 android.widget.TextView
or StaticLayout
. Since the text layout information will be included in this instance, android.widget.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 android.text.NoCopySpan
attached to the original text won't be passed to PrecomputedText.
Summary
Nested classes | |
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The information required for building |
Public methods | |
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open static PrecomputedTextCompat! |
create(@NonNull text: CharSequence, @NonNull params: PrecomputedTextCompat.Params) Create a new |
open Char | |
open Int |
Returns the count of paragraphs. |
open Int |
getParagraphEnd(@IntRange(0) paraIndex: Int) Returns the paragraph end offset of the text. |
open Int |
getParagraphStart(@IntRange(0) paraIndex: Int) Returns the paragraph start offset of the text. |
open PrecomputedTextCompat.Params |
Returns the parameters used to measure this text. |
open Int |
getSpanEnd(tag: Any!) |
open Int |
getSpanFlags(tag: Any!) |
open Int |
getSpanStart(tag: Any!) |
open Array<T>! | |
open static Future<PrecomputedTextCompat!>! |
getTextFuture(@NonNull charSequence: CharSequence, @NonNull params: PrecomputedTextCompat.Params, @Nullable executor: Executor?) Helper for PrecomputedText that returns a future to be used with |
open Int |
nextSpanTransition(start: Int, limit: Int, type: Class<Any!>!) |
open Unit |
removeSpan(what: Any!) |
open Unit | |
open CharSequence |
subSequence(startIndex: Int, endIndex: Int) |
open String |
toString() |
Properties | |
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open Int |
Public methods
create
open static fun create(
@NonNull text: CharSequence,
@NonNull params: PrecomputedTextCompat.Params
): PrecomputedTextCompat!
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 anyandroid.text.NoCopySpan
attached to the text won't be passed to the created PrecomputedText.
Parameters | |
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text |
CharSequence: the text to be measured |
params |
PrecomputedTextCompat.Params: parameters that define how text will be precomputed |
Return | |
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PrecomputedTextCompat! |
A PrecomputedText |
getParagraphEnd
@IntRange(0) open fun getParagraphEnd(@IntRange(0) paraIndex: Int): Int
Returns the paragraph end offset of the text.
getParagraphStart
@IntRange(0) open fun getParagraphStart(@IntRange(0) paraIndex: Int): Int
Returns the paragraph start offset of the text.
getParams
@NonNull open fun getParams(): PrecomputedTextCompat.Params
Returns the parameters used to measure this text.
getTextFuture
@UiThread open static fun getTextFuture(
@NonNull charSequence: CharSequence,
@NonNull params: PrecomputedTextCompat.Params,
@Nullable executor: Executor?
): Future<PrecomputedTextCompat!>!
Helper for PrecomputedText that returns a future to be used with androidx.appcompat.widget.AppCompatTextView#setTextFuture
. 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 androidx.appcompat.widget.AppCompatTextView#setTextFuture
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<precomputedtextcompat> future = PrecomputedTextCompat.getTextFuture( data.text, vh.textView.getTextMetricsParamsCompat(), myExecutor); // and pass future to TextView, which awaits result before measuring vh.textView.setTextFuture(future); } </precomputedtextcompat>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 | |
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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. |
Return | |
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Future<PrecomputedTextCompat!>! |
a future of the precomputed text |