This Repository shows the implement of Row-Layout, which is also called Flow-Layout, in Android. Detailed comments are provided among the codes.
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All views inside rowLayout viewgroup are filled in-row and automatically wrap.
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Child view is allowed to set its own margins.
Drawing the layout is a two pass process: a measure pass and a layout pass. The measuring pass is implemented in measure(int, int) and is a top-down traversal of the View tree. Each View pushes dimension specifications down the tree during the recursion. At the end of the measure pass, every View has stored its measurements. The second pass happens in layout(int, int, int, int) and is also top-down. During this pass each parent is responsible for positioning all of its children using the sizes computed in the measure pass.(More refer how-android-draws)
In general, the implement includes two main steps. Firstly, to get some feature varibles by measuring all children. Secondly, to specify each view's layout position according to the feature varibles.
Measurement is implemented by overridding the onMeasure() method. After all the child views are measured, we can accumulate the number of children under the constraint width of each row, and store each row's height which equals to the largest height among children's. Finally, we can set the largest width among all rows and the sum height of all rows as parents' measurement size.
Layout is implemented by overridding the onLayout() method. According to the list of the numbers of children in each row, we can layout each view into its corresponding row.
In addition, parent's padding and child views' margin need to be considered. The padding must involve in the measurement by calling getPaddingLeft(), getPaddingRight() and another two get methods. Three methods, generateLayoutParams(AttributeSet attrs), generateLayoutParams(LayoutParams p), generateDefaultLayoutParams() should be overrided in order to get child view's marginLayoutParams. Then, do not forget to add the margins which is from view's marginLayoutParams in when onlayout() is called.
Copyright (C) 2017. Henry Tam (Hosle)
Contact: hosle@163.com
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at
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