定义View元素和他们的属性

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最新推荐文章于 2024-08-20 22:52:05 发布

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分类专栏： learnandroid 文章标签： learn android

本文链接：https://blog.youkuaiyun.com/WAN_EXE/article/details/77932714

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本文介绍了Android布局中的核心元素View及其ViewGroup，详细讲解了TextView、ImageView等常见View的用法。重点讨论了View的标识符、高度和宽度设置，包括如何在运行时动态调整尺寸、使用尺寸单位dp以及设置内边距和外边距。同时，还提到了gravity和layout_gravity的作用，它们分别控制内容对齐和视图在父容器中的位置。

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Android上的布局就只有两种，一种是View和另外一种ViewGroup

ViewGroup就是前面文章中将到的三种Layout，决定了View的位置。

另外六种常见的View有

TextView displays a formatted text label
ImageView displays an image resource
Button can be clicked to perform an action
ImageButton displays a clickable image
EditText is an editable text field for user input
ListView is a scrollable list of items containing other views

View Identifiers

View Height and Width

<TextView
  android:layout_width="165dp" 
  android:layout_height="wrap_content" />

运行的时候改变view的属性

This can take the form of wrap_content (adjust height and width to the content size), match_parent (adjust height and width to the full size of the parent container), and a dimensions value such as 120dp. This can be changed at runtime in a number of ways:

// Change the width or height
int newInPixels = 50;
view.setLayoutParams(new LayoutParams(newInPixels, newInPixels));
// Trigger invalidation of the view to force adjustment
view.requestLayout();

Or we can change just the width or height individually:

int newDimensionInPixels = 50;
view.getLayoutParams().width = newDimensionInPixels;
view.getLayoutParams().height = newDimensionInPixels;
// Trigger invalidation of the view to force adjustment
view.requestLayout();

We can also set these dimensions in dp rather than pixels with:

int newDimensionInPixels = 50;
// convert to 50dp
int dimensionInDp = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, newDimensionInPixels, 
    getResources().getDisplayMetrics());
view.getLayoutParams().width = newDimensionInPixels;
view.getLayoutParams().height = dimensionInDp;
// Trigger invalidation of the view to force adjustment
view.requestLayout();

Layout Margin defines the amount of space around the outside of a view
Padding defines the amount of space around the contents or children of a view.

gravity determines the direction that the contents of a view will align (like CSS text-align).
layout_gravity determines the direction of the view within it's parent (like CSS float).

其它属性

Attribute	Description	Example Value
`android:background`	Background for the view	`#ffffff`
`android:onClick`	Method to invoke when clicked	`onButtonClicked`
`android:visibility`	Controls how view appears	`invisible`
`android:hint`	Hint text to display when empty	`@string/hint`
`android:text`	Text to display in view	`@string/foo`
`android:textColor`	Color of the text	`#000000`
`android:textSize`	Size of the text	`21sp`
`android:textStyle`	Style of the text formatting	`bold`