一、声明控件

1、如果你打开Android Studio后没有自动打开上一次创建的项目（比如我上次创建的是MyFirst App），看到的是图1所示的欢迎界面，直接找到项目点击打开即可

图1

2、打开后如图2，默认展示的是MainActivity.java，我们切换到activity_main.xml中，可以按住ctrl键（Mac系统是Command键）,然后鼠标单击第12行的“activity_main”；也可以通过左侧导航栏 res->layout->activity_main.xml双击打开

图2

3、切换后如图3，先看右上方框起来的部分，Android Studio布局支持三种设计模式，纯视图（就是现在看到这种）、视图+代码、纯代码，在纯视图模式下，我们可以直接从右侧控件区拖动控件到页面，可以实时的、直观的看到效果，通过拖动调整间距和位置，个人其实更喜欢split模式，即视图+代码，在通过代码添加控件的同时也能实时看到效果，我们点击split切换到视图+代码模式

图3

4、好，在图4中，粗糙的讲一下，这里系统默认的约束布局（ConstraintLayout），个人习惯使用线性布局（LinearLayout）和相对布局(RelativeLayout)，等我改一下

图4

5、改动后的代码如下，

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity"
    android:gravity="center"
    android:orientation="vertical">
    <TextView
        android:id="@+id/tv_text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" 
        android:text="Hello Word"
        android:textSize="22sp"/>
    <Button
        android:id="@+id/btn_change"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Click Me"/>

</LinearLayout>

欢迎大家来到IT世界,在知识的湖畔探索吧!

根结点下，我添加了“android:orientation=”vertical””，表示垂直方向布局，不添加这一句默认水平方向布局，即“android:orientation=”horizontal””
根结点下，添加了“android:gravity=”center””，表示布局中的控件居中
为TextView添加了id，并删除了末尾四个属性，因为那四个属性在约束布局下才生效
为TextView设置了默认显示文本和字体大小
添加了Button控件并设置了id

二、绑定控件

接下来我们切换回MainActivity.java,然后定义和绑定好控件

欢迎大家来到IT世界,在知识的湖畔探索吧!public class MainActivity extends AppCompatActivity {

    private TextView tvText;
    private Button btnChange;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initView();
    }

    private void initView() {
        tvText=findViewById(R.id.tv_text);
        btnChange=findViewById(R.id.btn_change);
    }
}

这里我定义了一个initView方法，并在方法体内进行的控件绑定；一是编码习惯，二是为了避免onCreate方法内看起来太杂太乱

三、通过点击按钮改变控件的显示文本

同理，添加setListener方法，设置btnChange的点击事件

private void setListener() {
    btnChange.setOnClickListener((v)->{
        tvText.setText("我是点击后的文本");
    });
}

别忘了在onCreate()方法里调用，即在“initView();”后添加“setListener();”；

四、TextView的其它属性

俗话说，我可以不用，但你必须得有，这不，TextView支持的属性我理解该有的它都有了，官网对于TextView属性介绍如下：

android:allowUndo	Whether undo should be allowed for editable text.
android:autoLink	Controls whether links such as urls and email addresses are automatically found and converted to clickable links.
android:autoSizeMaxTextSize	The maximum text size constraint to be used when auto-sizing text.
android:autoSizeMinTextSize	The minimum text size constraint to be used when auto-sizing text.
android:autoSizePresetSizes	Resource array of dimensions to be used in conjunction with autoSizeTextType set to uniform.
android:autoSizeStepGranularity	Specify the auto-size step size if autoSizeTextType is set to uniform.
android:autoSizeTextType	Specify the type of auto-size.
android:autoText	If set, specifies that this TextView has a textual input method and automatically corrects some common spelling errors.
android:breakStrategy	Break strategy (control over paragraph layout).
android:bufferType	Determines the minimum type that getText() will return.
android:capitalize	If set, specifies that this TextView has a textual input method and should automatically capitalize what the user types.
android:cursorVisible	Makes the cursor visible (the default) or invisible.
android:digits	If set, specifies that this TextView has a numeric input method and that these specific characters are the ones that it will accept.
android:drawableBottom	The drawable to be drawn below the text.
android:drawableEnd	The drawable to be drawn to the end of the text.
android:drawableLeft	The drawable to be drawn to the left of the text.
android:drawablePadding	The padding between the drawables and the text.
android:drawableRight	The drawable to be drawn to the right of the text.
android:drawableStart	The drawable to be drawn to the start of the text.
android:drawableTint	Tint to apply to the compound (left, top, etc.) drawables.
android:drawableTintMode	Blending mode used to apply the compound (left, top, etc.) drawables tint.
android:drawableTop	The drawable to be drawn above the text.
android:editable	If set, specifies that this TextView has an input method.
android:editorExtras	Reference to an <input-extras> XML resource containing additional data to supply to an input method, which is private to the implementation of the input method.
android:elegantTextHeight	Elegant text height, especially for less compacted complex script text.
android:ellipsize	If set, causes words that are longer than the view is wide to be ellipsized instead of broken in the middle.
android:ems	Makes the TextView be exactly this many ems wide.
android:enabled	Specifies whether the widget is enabled.
android:fallbackLineSpacing	Whether to respect the ascent and descent of the fallback fonts that are used in displaying the text.
android:firstBaselineToTopHeight	Distance from the top of the TextView to the first text baseline.
android:fontFamily	Font family (named by string or as a font resource reference) for the text.
android:fontFeatureSettings	Font feature settings.
android:fontVariationSettings	Font variation settings.
android:freezesText	If set, the text view will include its current complete text inside of its frozen icicle in addition to meta-data such as the current cursor position.
android:gravity	Specifies how to align the text by the view’s x- and/or y-axis when the text is smaller than the view.
android:height	Makes the TextView be exactly this tall.
android:hint	Hint text to display when the text is empty.
android:hyphenationFrequency	Frequency of automatic hyphenation.
android:imeActionId	Supply a value for EditorInfo.actionId used when an input method is connected to the text view.
android:imeActionLabel	Supply a value for EditorInfo.actionLabel used when an input method is connected to the text view.
android:imeOptions	Additional features you can enable in an IME associated with an editor to improve the integration with your application.
android:includeFontPadding	Leave enough room for ascenders and descenders instead of using the font ascent and descent strictly.
android:inputMethod	If set, specifies that this TextView should use the specified input method (specified by fully-qualified class name).
android:inputType	The type of data being placed in a text field, used to help an input method decide how to let the user enter text.
android:justificationMode	Mode for justification.
android:lastBaselineToBottomHeight	Distance from the bottom of the TextView to the last text baseline.
android:letterSpacing	Text letter-spacing.
android:lineBreakStyle	Indicates the line break strategies can be used when calculating the text wrapping.
android:lineBreakWordStyle	Specify the phrase-based line break can be used when calculating the text wrapping.
android:lineHeight	Explicit height between lines of text.
android:lineSpacingExtra	Extra spacing between lines of text.
android:lineSpacingMultiplier	Extra spacing between lines of text, as a multiplier.
android:lines	Makes the TextView be exactly this many lines tall.
android:linksClickable	If set to false, keeps the movement method from being set to the link movement method even if autoLink causes links to be found.
android:marqueeRepeatLimit	The number of times to repeat the marquee animation.
android:maxEms	Makes the TextView be at most this many ems wide.
android:maxHeight	Makes the TextView be at most this many pixels tall.
android:maxLength	Set an input filter to constrain the text length to the specified number.
android:maxLines	Makes the TextView be at most this many lines tall.
android:maxWidth	Makes the TextView be at most this many pixels wide.
android:minEms	Makes the TextView be at least this many ems wide.
android:minHeight	Makes the TextView be at least this many pixels tall.
android:minLines	Makes the TextView be at least this many lines tall.
android:minWidth	Makes the TextView be at least this many pixels wide.
android:numeric	If set, specifies that this TextView has a numeric input method.
android:password	Whether the characters of the field are displayed as password dots instead of themselves.
android:phoneNumber	If set, specifies that this TextView has a phone number input method.
android:privateImeOptions	An addition content type description to supply to the input method attached to the text view, which is private to the implementation of the input method.
android:scrollHorizontally	Whether the text is allowed to be wider than the view (and therefore can be scrolled horizontally).
android:selectAllOnFocus	If the text is selectable, select it all when the view takes focus.
android:shadowColor	Place a blurred shadow of text underneath the text, drawn with the specified color.
android:shadowDx	Horizontal offset of the text shadow.
android:shadowDy	Vertical offset of the text shadow.
android:shadowRadius	Blur radius of the text shadow.
android:singleLine	Constrains the text to a single horizontally scrolling line instead of letting it wrap onto multiple lines, and advances focus instead of inserting a newline when you press the enter key.
android:text	Text to display.
android:textAllCaps	Present the text in ALL CAPS.
android:textAppearance	Base text color, typeface, size, and style.
android:textColor	Text color.
android:textColorHighlight	Color of the text selection highlight.
android:textColorHint	Color of the hint text.
android:textColorLink	Text color for links.
android:textCursorDrawable	Reference to a drawable that will be drawn under the insertion cursor.
android:textFontWeight	Weight for the font used in the TextView.
android:textIsSelectable	Indicates that the content of a non-editable text can be selected.
android:textScaleX	Sets the horizontal scaling factor for the text.
android:textSelectHandle	Reference to a drawable that will be used to display a text selection anchor for positioning the cursor within text.
android:textSelectHandleLeft	Reference to a drawable that will be used to display a text selection anchor on the left side of a selection region.
android:textSelectHandleRight	Reference to a drawable that will be used to display a text selection anchor on the right side of a selection region.
android:textSize	Size of the text.
android:textStyle	Style (normal, bold, italic, bold\|italic) for the text.
android:typeface	Typeface (normal, sans, serif, monospace) for the text.
android:width	Makes the TextView be exactly this wide.

五、Button支持的其它属性

官网对于Button的属性没有列出，因为它本质上就是一个TextView，只不过封装了一下

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