Android LinearLayout实现自动换行效果

发布时间：2020-09-13 14:19:34

来源：脚本之家

阅读：431

作者：星辰之力

在我们开发过程中会经常遇见一些客户要求但是Android系统又不提供的效果，这时我们只能自己动手去实现它，或者从网络上借鉴他人的资源，本着用别人不如自己会做的心态，在此我总结了一下Android中如何实现自动换行的LinearLayout。

在本文中，说是LinearLayout其实是继承自GroupView，在这里主要重写了两个方法，onMeasure、onLayout方法，下面我对此加以介绍。(代码中使用了AttributeSet，由于时间问题不再予以介绍)。

1. onMeasure是干什么的？

在ViewGroup的创建过程中，onMeasure是在onLayout之前的，所以在此先对onMeasure进行介绍，onMeasure方法是计算子控件与父控件在屏幕中所占长宽大小的，onMeasure传入两个参数——widthMeasureSpec和heightMeasureSpec. 这两个参数指明控件可获得的空间以及关于这个空间描述的元数据.

int withMode = MeasureSpec.getMode(widthMeasureSpec);

int withSize = MeasureSpec.getSize(widthMeasureSpec);

int heightMode = MeasureSpec.getMode(heightMeasureSpec);

int heightSize = MeasureSpec.getSize(heightMeasureSpec);

Mode有3种模式分别是UNSPECIFIED, EXACTLY和AT_MOST，如果是AT_MOST，Size代表的是最大可获得的空间；如果是EXACTLY，Size代表的是精确的尺寸；如果是UNSPECIFIED，就是你想要多少就有多少。经过代码测试就知道，当我们设置width或height为fill_parent时，容器在布局时调用子 view的measure方法传入的模式是EXACTLY，因为子view会占据剩余容器的空间，所以它大小是确定的。而当设置为 wrap_content时，容器传进去的是AT_MOST, 表示子view的大小最多是多少，这样子view会根据这个上限来设置自己的尺寸。当子view的大小设置为精确值时，容器传入的是EXACTLY。

2. onLayout是干什么的？

与onMesaure相比，onLayout更加容易理解，它的作用就是调座位，就是把所有的子View根据不同的需要，通过View. layout(int l, int t, int r, int b)方法指定它所在的位置。

3. 解决问题

只要对onMeasure和onLayout加以理解，对于该篇所要实现的功能就不再难以实现，下面贴上代码，并在代码中讲解。

WaroLinearLayout.java

public class WarpLinearLayout extends ViewGroup {

private Type mType;

private List mWarpLineGroup;

public WarpLinearLayout(Context context) {

this(context, null);

}

public WarpLinearLayout(Context context, AttributeSet attrs) {

this(context, attrs, R.style.WarpLinearLayoutDefault);

}

public WarpLinearLayout(Context context, AttributeSet attrs, int defStyleAttr) {

super(context, attrs, defStyleAttr);

mType = new Type(context, attrs);

}

@Override

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

int withMode = MeasureSpec.getMode(widthMeasureSpec);

int withSize = MeasureSpec.getSize(widthMeasureSpec);

int heightMode = MeasureSpec.getMode(heightMeasureSpec);

int heightSize = MeasureSpec.getSize(heightMeasureSpec);

int with = 0;

int height = 0;

int childCount = getChildCount();

/**

* 在调用childView。getMeasre之前必须先调用该行代码，用于对子View大小的测量

*/

measureChildren(widthMeasureSpec, heightMeasureSpec);

/**

* 计算宽度

*/

switch (withMode) {

case MeasureSpec.EXACTLY:

with = withSize;

break;

case MeasureSpec.AT_MOST:

for (int i = 0; i < childCount; i++) {

if (i != 0) {

with += mType.horizontal_Space;

}

with += getChildAt(i).getMeasuredWidth();

}

with += getPaddingLeft() + getPaddingRight();

with = with > withSize ? withSize : with;

break;

case MeasureSpec.UNSPECIFIED:

for (int i = 0; i < childCount; i++) {

if (i != 0) {

with += mType.horizontal_Space;

}

with += getChildAt(i).getMeasuredWidth();

}

with += getPaddingLeft() + getPaddingRight();

break;

default:

with = withSize;

break;

}

/**

* 根据计算出的宽度，计算出所需要的行数

*/

WarpLine warpLine = new WarpLine();

/**

* 不能够在定义属性时初始化，因为onMeasure方法会多次调用

*/

mWarpLineGroup = new ArrayList();

for (int i = 0; i < childCount; i++) {

if (warpLine.lineWidth + getChildAt(i).getMeasuredWidth() + mType.horizontal_Space > with) {

if (warpLine.lineView.size() == 0) {

warpLine.addView(getChildAt(i));

mWarpLineGroup.add(warpLine);

warpLine = new WarpLine();

} else {

mWarpLineGroup.add(warpLine);

warpLine = new WarpLine();

warpLine.addView(getChildAt(i));

}

} else {

warpLine.addView(getChildAt(i));

}

}

/**

* 添加最后一行

*/

if (warpLine.lineView.size() > 0 && !mWarpLineGroup.contains(warpLine)) {

mWarpLineGroup.add(warpLine);

}

/**

* 计算宽度

*/

height = getPaddingTop() + getPaddingBottom();

for (int i = 0; i < mWarpLineGroup.size(); i++) {

if (i != 0) {

height += mType.vertical_Space;

}

height += mWarpLineGroup.get(i).height;

}

switch (heightMode) {

case MeasureSpec.EXACTLY:

height = heightSize;

break;

case MeasureSpec.AT_MOST:

height = height > heightSize ? heightSize : height;

break;

case MeasureSpec.UNSPECIFIED:

break;

default:

break;

}

setMeasuredDimension(with, height);

}

@Override

protected void onLayout(boolean changed, int l, int t, int r, int b) {

t = getPaddingTop();

for (int i = 0; i < mWarpLineGroup.size(); i++) {

int left = getPaddingLeft();

WarpLine warpLine = mWarpLineGroup.get(i);

int lastWidth = getMeasuredWidth() - warpLine.lineWidth;

for (int j = 0; j < warpLine.lineView.size(); j++) {

View view = warpLine.lineView.get(j);

if (isFull()) {//需要充满当前行时

view.layout(left, t, left + view.getMeasuredWidth() + lastWidth / warpLine.lineView.size(), t + view.getMeasuredHeight());

left += view.getMeasuredWidth() + mType.horizontal_Space + lastWidth / warpLine.lineView.size();

} else {

switch (getGrivate()) {

case 0://右对齐

view.layout(left + lastWidth, t, left + lastWidth + view.getMeasuredWidth(), t + view.getMeasuredHeight());

break;

case 2://居中对齐

view.layout(left + lastWidth / 2, t, left + lastWidth / 2 + view.getMeasuredWidth(), t + view.getMeasuredHeight());

break;

default://左对齐

view.layout(left, t, left + view.getMeasuredWidth(), t + view.getMeasuredHeight());

break;

}

left += view.getMeasuredWidth() + mType.horizontal_Space;

}

}

t += warpLine.height + mType.vertical_Space;

}

}

/**

* 用于存放一行子View

*/

private final class WarpLine {

private List lineView = new ArrayList();

/**

* 当前行中所需要占用的宽度

*/

private int lineWidth = getPaddingLeft() + getPaddingRight();

/**

* 该行View中所需要占用的最大高度

*/

private int height = 0;

private void addView(View view) {

if (lineView.size() != 0) {

lineWidth += mType.horizontal_Space;

}

height = height > view.getMeasuredHeight() ? height : view.getMeasuredHeight();

lineWidth += view.getMeasuredWidth();

lineView.add(view);

}

}

/**

* 对样式的初始化

*/

private final static class Type {

/*

*对齐方式 right 0，left 1，center 2

*/

private int grivate;

/**

* 水平间距,单位px

*/

private float horizontal_Space;

/**

* 垂直间距,单位px

*/

private float vertical_Space;

/**

* 是否自动填满

*/

private boolean isFull;

Type(Context context, AttributeSet attrs) {

if (attrs == null) {

return;

}

TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.WarpLinearLayout);

grivate = typedArray.getInt(R.styleable.WarpLinearLayout_grivate, grivate);

horizontal_Space = typedArray.getDimension(R.styleable.WarpLinearLayout_horizontal_Space, horizontal_Space);

vertical_Space = typedArray.getDimension(R.styleable.WarpLinearLayout_vertical_Space, vertical_Space);

isFull = typedArray.getBoolean(R.styleable.WarpLinearLayout_isFull, isFull);

}

}

public int getGrivate() {

return mType.grivate;

}

public float getHorizontal_Space() {

return mType.horizontal_Space;

}

public float getVertical_Space() {

return mType.vertical_Space;

}

public boolean isFull() {

return mType.isFull;

}

public void setGrivate(int grivate) {

mType.grivate = grivate;

}

public void setHorizontal_Space(float horizontal_Space) {

mType.horizontal_Space = horizontal_Space;

}

public void setVertical_Space(float vertical_Space) {

mType.vertical_Space = vertical_Space;

}

public void setIsFull(boolean isFull) {

mType.isFull = isFull;

}

/**

* 每行子View的对齐方式

*/

public final static class Gravite {

public final static int RIGHT = 0;

public final static int LEFT = 1;

public final static int CENTER = 2;

}

}

attrs.xml

WarpLinearLayoutDefault

left

20dp

20dp

false

MainActivity.java

public class MainActivity extends Activity {

private Button btn;

private WarpLinearLayout warpLinearLayout;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

btn = (Button) findViewById(R.id.btn);

warpLinearLayout = (WarpLinearLayout) findViewById(R.id.warpLinearLayout);

btn.setOnClickListener(new View.OnClickListener() {

@Override

public void onClick(View v) {

int n = new Random().nextInt(10) + 5;

StringBuffer stringBuffer = new StringBuffer();

Random random = new Random();

Log.i("WarpLinearLayout","n="+n);

for (int i = 0; i < n; i++) {

stringBuffer.append((char)(65+random.nextInt(26)));

Log.i("WarpLinearLayout", "StringBuffer=" + stringBuffer.toString());

}

TextView tv = new TextView(MainActivity.this);

tv.setText(stringBuffer.toString()+"000");

tv.setBackgroundResource(R.drawable.radius_backgroup_yellow);

tv.setPadding(10,10,10,10);

warpLinearLayout.addView(tv);

}

});

}

}

activity_main.xml

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"

android:paddingBottom="@dimen/activity_vertical_margin"

android:paddingLeft="@dimen/activity_horizontal_margin"

android:paddingRight="@dimen/activity_horizontal_margin"

android:paddingTop="@dimen/activity_vertical_margin"

tools:context=".MainActivity">

android:id="@+id/btn"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:gravity="center"

android:text="add"

android:textSize="20dp" />

android:id="@+id/warpLinearLayout"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:layout_below="@id/btn"

android:background="#FF00FF00"

android:padding="10dp"

app:grivate="right"

app:horizontal_Space="10dp"

app:isFull="false"

app:vertical_Space="10dp">

运行效果图如下：

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持亿速云。