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在我們開發過程中會經常遇見一些客戶要求但是Android系統又不提供的效果，這時我們只能自己動手去實現它，或者從網絡上借鑒他人的資源，本著用別人不如自己會做的心態，在此我總結了一下Android中如何實現自動換行的LinearLayout。
在本文中，說是LinearLayout其實是繼承自GroupView，在這里主要重寫了兩個方法，onMeasure、onLayout方法，下面我對此加以介紹。（代碼中使用了AttributeSet，由于時間問題不再予以介紹）。
1. onMeasure是干什么的？
在ViewGroup的創建過程中，onMeasure是在onLayout之前的，所以在此先對onMeasure進行介紹，onMeasure方法是計算子控件與父控件在屏幕中所占長寬大小的，onMeasure傳入兩個參數——widthMeasureSpec和heightMeasureSpec. 這兩個參數指明控件可獲得的空間以及關于這個空間描述的元數據.
int withMode = MeasureSpec.getMode(widthMeasureSpec); int withSize = MeasureSpec.getSize(widthMeasureSpec); int heightMode = MeasureSpec.getMode(heightMeasureSpec); int heightSize = MeasureSpec.getSize(heightMeasureSpec);
Mode有3種模式分別是UNSPECIFIED, EXACTLY和AT_MOST，如果是AT_MOST，Size代表的是最大可獲得的空間；如果是EXACTLY，Size代表的是精確的尺寸；如果是UNSPECIFIED，就是你想要多少就有多少。經過代碼測試就知道，當我們設置width或height為fill_parent時，容器在布局時調用子 view的measure方法傳入的模式是EXACTLY，因為子view會占據剩余容器的空間，所以它大小是確定的。而當設置為 wrap_content時，容器傳進去的是AT_MOST, 表示子view的大小最多是多少，這樣子view會根據這個上限來設置自己的尺寸。當子view的大小設置為精確值時，容器傳入的是EXACTLY。
2. onLayout是干什么的？
與onMesaure相比，onLayout更加容易理解，它的作用就是調座位，就是把所有的子View根據不同的需要，通過View. layout(int l, int t, int r, int b)方法指定它所在的位置。
3. 解決問題
只要對onMeasure和onLayout加以理解，對于該篇所要實現的功能就不再難以實現，下面貼上代碼，并在代碼中講解。
WaroLinearLayout.java
public class WarpLinearLayout extends ViewGroup {
private Type mType;
private List<WarpLine> 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();
/**
* 在調用childView。getMeasre之前必須先調用該行代碼，用于對子View大小的測量
*/
measureChildren(widthMeasureSpec, heightMeasureSpec);
/**
* 計算寬度
*/
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;
}
/**
* 根據計算出的寬度，計算出所需要的行數
*/
WarpLine warpLine = new WarpLine();
/**
* 不能夠在定義屬性時初始化，因為onMeasure方法會多次調用
*/
mWarpLineGroup = new ArrayList<WarpLine>();
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);
}
/**
* 計算寬度
*/
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()) {//需要充滿當前行時
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://右對齊
view.layout(left + lastWidth, t, left + lastWidth + view.getMeasuredWidth(), t + view.getMeasuredHeight());
break;
case 2://居中對齊
view.layout(left + lastWidth / 2, t, left + lastWidth / 2 + view.getMeasuredWidth(), t + view.getMeasuredHeight());
break;
default://左對齊
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<View> lineView = new ArrayList<View>();
/**
* 當前行中所需要占用的寬度
*/
private int lineWidth = getPaddingLeft() + getPaddingRight();
/**
* 該行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);
}
}
/**
* 對樣式的初始化
*/
private final static class Type {
/*
*對齊方式 right 0，left 1，center 2
*/
private int grivate;
/**
* 水平間距,單位px
*/
private float horizontal_Space;
/**
* 垂直間距,單位px
*/
private float vertical_Space;
/**
* 是否自動填滿
*/
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的對齊方式
*/
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
<?xml version="1.0" encoding="utf-8"?>
<resources>
<declare-styleable name="WarpLinearLayout">
<attr name="grivate" format="enum"><!--對齊方式 !-->
<enum name="right" value="0"></enum>
<enum name="left" value="1"></enum>
<enum name="center" value="2"></enum>
</attr>
<attr name="horizontal_Space" format="dimension"></attr>
<attr name="vertical_Space" format="dimension"></attr>
<attr name="isFull" format="boolean"></attr>
</declare-styleable>
</resources>
WarpLinearLayoutDefault
<style name="WarpLinearLayoutDefault">
<item name="grivate">left</item>
<item name="horizontal_Space">20dp</item>
<item name="vertical_Space">20dp</item>
<item name="isFull">false</item>
</style>
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
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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"
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">
<Button
android:id="@+id/btn"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:text="add"
android:textSize="20dp" />
<com.example.customview.viewgroup.WarpLinearLayout
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"></com.example.customview.viewgroup.WarpLinearLayout>
</RelativeLayout>
運行效果圖如下：
以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持億速云。
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