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README.md

      1 Drawing a rounded corner background on text
      2 ============
      3 
      4 This sample shows how to draw a **rounded** corner background on text. It supports the following cases:
      5 
      6 * Set the background on **one line** text
      7 
      8 <img src="../screenshots/single.png" width="30%" />
      9 
     10 * Set the background on text over **two or multiple lines**
     11 
     12 <img src="../screenshots/multi.png" width="30%" />
     13 
     14 * Set the background on **right-to-left** text
     15 
     16 <img src="../screenshots/rtl.png" width="30%" />
     17 
     18 
     19 Implementation
     20 ---------------
     21 Depending on the position of the text, we need to draw four different drawables as text backgrounds:
     22 
     23 * Text fits on one line: we only need one drawable
     24 * Text fits on 2 lines: we need drawables for the start and end of the text
     25 * Text spans multiple lines: we need drawables for the start, middle and end of the text
     26 
     27 <img src="../screenshots/lines.png" width="30%" />
     28 
     29 The four drawables that need to be drawn depending on the position of the text:
     30 
     31 To position the background, we need to:
     32 * Determine whether the text spans multiple lines
     33 * Find the start and end lines
     34 * Find the start and end offset depending on the paragraph direction
     35 
     36 All of these can be computed based on the text Layout. To render the background behind the text we need access to the Canvas. A custom TextView has access to all of the information necessary to position the drawables and render them.
     37 
     38 Our solution involves splitting our problem into 4 parts and creating classes dealing with them individually:
     39 * **Marking the position of the background** is done in the XML resources via Annotation spans and then, in the code, we read them in the `TextRoundedBgHelper`
     40 * Providing the background **drawables as attributes** of the TextView - implemented in `TextRoundedBgAttributeReader`
     41 * **Rendering the drawables** depending on whether the text runs across **one or multiple lines** - `TextRoundedBgHelper` interface and its implementations: `SingleLineRenderer` and `MultiLineRenderer`
     42 * Supporting **custom drawing** on a TextView - `RoundedBgTextView`, a class that extends `AppCompatTextView`, reads the attributes with the help of `TextRoundedBgAttributeReader`, overrides `onDraw` where it uses `TextRoundedBgHelper` to draw the background.
     43 
     44 Getting Started
     45 ---------------
     46 
     47 Clone this repository, enter the top level directory and run `./gradlew tasks`
     48 to get an overview of all the tasks available for this project.
     49 
     50 Some important tasks are:
     51 
     52 ```
     53 assembleDebug - Assembles all Debug builds.
     54 installDebug - Installs the Debug build.
     55 connectedAndroidTest - Installs and runs the tests for Debug build on connected
     56 devices.
     57 test - Run all unit tests.
     58 ```
     59 
     60 Screenshots
     61 -----------
     62 <img src="../screenshots/rounded_bg.png" width="30%" />
     63 
     64 Support
     65 -------
     66 - Stack Overflow: http://stackoverflow.com/questions/tagged/android-text
     67 
     68 If you've found an error in this sample, please file an issue:
     69 https://github.com/googlesamples/android-text/issues
     70 
     71 Patches are encouraged, and may be submitted by forking this project and
     72 submitting a pull request through GitHub.
     73 
     74 License
     75 --------
     76 ```
     77 Copyright 2018 The Android Open Source Project
     78 
     79 Licensed to the Apache Software Foundation (ASF) under one or more contributor
     80 license agreements. See the NOTICE file distributed with this work for
     81 additional information regarding copyright ownership. The ASF licenses this
     82 file to you under the Apache License, Version 2.0 (the "License"); you may not
     83 use this file except in compliance with the License. You may obtain a copy of
     84 the License at
     85 
     86    http://www.apache.org/licenses/LICENSE-2.0
     87 
     88 Unless required by applicable law or agreed to in writing, software
     89 distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
     90 WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
     91 License for the specific language governing permissions and limitations under
     92 the License.
     93 ```
     94