Android View measure (五) 支持margin属性,从一个异常说起
来源:互联网 发布:靠谱的网络招聘平台 编辑:程序博客网 时间:2024/06/06 01:03
先来看下代码
继承自ViewGroup,主要是演示自定义视图中如何支持margin属性,重点在child.getLayoutParams()一行,接下来看下布局文件中如何使用
2. 布局文件
重头戏:android:layout_margin="10dip" margin属性
出现以上异常的原因,LayoutParams从哪里来的?
视图的加载有两种方式一种是代码addView 一种是inflate 。
1. inflate 方法加载并添加LayoutParams
Android中measure过程、WRAP_CONTENT详解以及xml布局文件解析流程浅析(上)
以下是关键
通过查看以上addView添加LayoutParams代码可以发现解决方案,复写这些函数,创建当前自定义视图的LayoutParams继承自MarginLayoutParams。
一、查看夏目
1. 自定义控件- public class CustomViewGroup extends ViewGroup {
- ......
- @Override
- protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
- super.onMeasure(widthMeasureSpec, heightMeasureSpec);
- // 遍历所有子视图,进行measure操作
- for (int i = 0; i < getChildCount(); i++) {
- View child = getChildAt(i);
- if (child != null && child.getVisibility() != View.GONE) {
- measureChild(child, widthMeasureSpec, heightMeasureSpec);
- // 支持子视图设置的android:layout_margin属性
- MarginLayoutParams layoutParams = (MarginLayoutParams) child.getLayoutParams();
- int marginLeft = layoutParams.leftMargin;
- }
- }
- setMeasuredDimension(widthMeasureSpec, heightMeasureSpec);
- }
- @Override
- protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
- for (int i = 0; i < getChildCount(); i++) {
- View childView = getChildAt(i);
- // 只为最简单代码复现BUG,所有子视图都随便放
- childView.layout(left, top, left + childView.getMeasuredWidth(), top + childView.getMeasuredHeight());
- }
- }
- }
继承自ViewGroup,主要是演示自定义视图中如何支持margin属性,重点在child.getLayoutParams()一行,接下来看下布局文件中如何使用
2. 布局文件
- <com.example.android.apis.CustomViewGroup
- android:id="@+id/custom_view_group"
- android:layout_width="match_parent"
- android:layout_height="wrap_content" >
- <TextView
- android:layout_width="wrap_content"
- android:layout_height="wrap_content"
- oid:layout_margin="10dip"
- android:text="love_world_" />
- </com.example.android.apis.CustomViewGroup>
重头戏:android:layout_margin="10dip" margin属性
- java.lang.ClassCastException: android.view.ViewGroup$LayoutParams cannot be cast to android.view.ViewGroup$MarginLayoutParams
- at com.example.android.apis.CustomViewGroup.onMeasure(CustomViewGroup.java:50)
- at android.view.View.measure(View.java:16831)
- at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5245)
- at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1410)
- at android.widget.LinearLayout.measureHorizontal(LinearLayout.java:1052)
- at android.widget.LinearLayout.onMeasure(LinearLayout.java:590)
- at android.view.View.measure(View.java:16831)
- at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5245)
- at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1410)
- at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
- at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
- at android.view.View.measure(View.java:16831)
- at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5245)
- at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
- at android.view.View.measure(View.java:16831)
- at android.widget.LinearLayout.measureVertical(LinearLayout.java:847)
- at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
- at android.view.View.measure(View.java:16831)
- at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5245)
- at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
- at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2586)
- at android.view.View.measure(View.java:16831)
- at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2189)
- at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1352)
- at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1535)
- at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1249)
- at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6364)
- at android.view.Choreographer$CallbackRecord.run(Choreographer.java:791)
- at android.view.Choreographer.doCallbacks(Choreographer.java:591)
- at android.view.Choreographer.doFrame(Choreographer.java:561)
- at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:777)
- at android.os.Handler.handleCallback(Handler.java:730)
- at android.os.Handler.dispatchMessage(Handler.java:92)
- at android.os.Looper.loop(Looper.java:176)
- at android.app.ActivityThread.main(ActivityThread.java:5419)
- at java.lang.reflect.Method.invokeNative(Native Method)
- at java.lang.reflect.Method.invoke(Method.java:525)
- at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1209)
- at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1025)
- at dalvik.system.NativeStart.main(Native Method)
出现以上异常的原因,LayoutParams从哪里来的?
视图的加载有两种方式一种是代码addView 一种是inflate 。
1. inflate 方法加载并添加LayoutParams
Android中measure过程、WRAP_CONTENT详解以及xml布局文件解析流程浅析(上)
- public class MainActivity extends Activity {
- @Override
- protected void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.activity_main);
- CustomViewGroup customViewGroup = (CustomViewGroup) findViewById(R.id.custom_view_group);
- customViewGroup.addView(createTextView("Love_world_"));
- }
- private View createTextView(String value) {
- TextView textView = new TextView(this);
- textView.setText("a child view");
- textView.setText(value);
- textView.setLayoutParams(new ViewGroup.MarginLayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT));
- return textView;
- }
- }
2. ViewGroup.addView源码,查找何处添加LayoutParams
- public abstract class ViewGroup extends View implements ViewParent, ViewManager {
- public void addView(View child) {
- addView(child, -1);
- }
- public void addView(View child, int index) {
- LayoutParams params = child.getLayoutParams();
- // 子视图LayoutParams为为空是处理方式
- if (params == null) {
- params = generateDefaultLayoutParams();
- if (params == null) {
- throw new IllegalArgumentException("generateDefaultLayoutParams() cannot return null");
- }
- }
- addView(child, index, params);
- }
- public void addView(View child, int width, int height) {
- final LayoutParams params = generateDefaultLayoutParams();
- params.width = width;
- params.height = height;
- addView(child, -1, params);
- }
- public void addView(View child, LayoutParams params) {
- addView(child, -1, params);
- }
- public void addView(View child, int index, LayoutParams params) {
- if (DBG) {
- System.out.println(this + " addView");
- }
- // addViewInner() will call child.requestLayout() when setting the new LayoutParams
- // therefore, we call requestLayout() on ourselves before, so that the child's request
- // will be blocked at our level
- requestLayout();
- invalidate();
- addViewInner(child, index, params, false);
- }
- // 子视图默认LayoutParams实例
- protected LayoutParams generateDefaultLayoutParams() {
- return new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
- }
- // 定义LayoutParams类
- public static class LayoutParams {
- public int width;
- public int height;
- public LayoutParams(int width, int height) {
- this.width = width;
- this.height = height;
- }
- }
- }
以下是关键
- public abstract class ViewGroup extends View implements ViewParent, ViewManager {
- private void addViewInner(View child, int index, LayoutParams params,
- boolean preventRequestLayout) {
- if (child.getParent() != null) {
- throw new IllegalStateException("The specified child already has a parent. " +
- "You must call removeView() on the child's parent first.");
- }
- if (!checkLayoutParams(params)) {
- params = generateLayoutParams(params);
- }
- if (preventRequestLayout) {
- child.mLayoutParams = params;
- } else {
- child.setLayoutParams(params);
- }
- ......
- }
- protected boolean checkLayoutParams(ViewGroup.LayoutParams p) {
- return p != null;
- }
- }
通过查看以上addView添加LayoutParams代码可以发现解决方案,复写这些函数,创建当前自定义视图的LayoutParams继承自MarginLayoutParams。
- public class CustomViewGroup extends ViewGroup {
- @Override
- protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
- ......
- }
- @Override
- protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
- ......
- }
- @Override
- protected LayoutParams generateLayoutParams(ViewGroup.LayoutParams p) {
- return new LayoutParams(p);
- }
- @Override
- protected LayoutParams generateDefaultLayoutParams() {
- return new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT);
- }
- @Override
- public LayoutParams generateLayoutParams(AttributeSet attrs) {
- return new LayoutParams(getContext(), attrs);
- }
- // 继承自margin,支持子视图android:layout_margin属性
- public static class LayoutParams extends MarginLayoutParams {
- public LayoutParams(Context c, AttributeSet attrs) {
- super(c, attrs);
- }
- public LayoutParams(int width, int height) {
- super(width, height);
- }
- public LayoutParams(ViewGroup.LayoutParams source) {
- super(source);
- }
- public LayoutParams(ViewGroup.MarginLayoutParams source) {
- super(source);
- }
- }
- }
0 0
- Android View measure (五) 支持margin属性,从一个异常说起
- Android View measure (五) 支持margin属性,从一个异常说起
- MVP浅尝----从一个自定义View说起
- Android View体系(七)从源码解析View的measure流程
- Android从捕获全局异常说起
- Android View measure (二) 自定义UI控件measure相关
- android 4.3 调用 view.measure()时报空指针异常
- Android View measure (一) 流程分析
- Android View measure (三) 常用方法
- android View.measure
- Android View measure过程
- android View.measure()初探
- Android View的Measure
- Android View-measure
- Android 从0开始自定义控件之 View 的 measure 过程(七)
- Android的自动化测试五:从单元测试说起
- 从一个小程序说起(1)
- 从一个“Bug”说起
- 【matlab】频域滤波函数lpfilt()
- 二叉树相关
- java父类子类中静态非静态的关系
- Windows10修复 .NET FrameWork3.5
- poj3624
- Android View measure (五) 支持margin属性,从一个异常说起
- Word 2013 参考文献插入及交叉引用的实现方法
- myeclipse常用快捷键集
- IOS开发之UIFont应用
- 前馈神经网络与深度学习概述
- Java类集
- each_with_object
- mysql linux免编译版 安装教程
- HTML事件