LayoutInflater和LayoutParams

最新推荐文章于 2025-03-30 23:11:49 发布

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本文深入解析LayoutInflater的工作原理，包括其在Android系统中的注册与实现过程，以及PhoneLayoutInflater类的onCreateView方法如何创建View。同时，阐述了LayoutParams类的功能，它是如何在ViewGroup中为子视图设置布局参数，包括高度、宽度及margin属性。

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一.LayoutInflater

开发时，很多时候会用到LayoutInflater来加载指定的布局

LayoutInflater inflater = (LayoutInflater)context.getSystemService
       (Context.LAYOUT_INFLATER_SERVICE);
// 或者通过from(Context context)获取实例
LayoutInflater inflater = LayoutInflater.from(context);

inflater.inflate(int resource, ViewGroup root);

在frameworks的SystemServiceRegistry.java中注册了此服务

        registerService(Context.LAYOUT_INFLATER_SERVICE, LayoutInflater.class,
                new CachedServiceFetcher<LayoutInflater>() {
            @Override
            public LayoutInflater createService(ContextImpl ctx) {
                return new PhoneLayoutInflater(ctx.getOuterContext());
            }});

new PhoneLayoutInflater，PhoneLayoutInflater继承了LayoutInflater

LayoutInflater是一个抽象类：

public abstract class LayoutInflater {
    ....
}

PhoneLayoutInflater：

public class PhoneLayoutInflater extends LayoutInflater {
    private static final String[] sClassPrefixList = {
        "android.widget.",
        "android.webkit.",
        "android.app."
    };

    /**
     * Instead of instantiating directly, you should retrieve an instance
     * through {@link Context#getSystemService}
     *
     * @param context The Context in which in which to find resources and other
     *                application-specific things.
     *
     * @see Context#getSystemService
     */
    public PhoneLayoutInflater(Context context) {
        super(context);
    }

    protected PhoneLayoutInflater(LayoutInflater original, Context newContext) {
        super(original, newContext);
    }

    /** Override onCreateView to instantiate names that correspond to the
        widgets known to the Widget factory. If we don't find a match,
        call through to our super class.
    */
    @Override protected View onCreateView(String name, AttributeSet attrs) throws ClassNotFoundException {
        for (String prefix : sClassPrefixList) {
            try {
                View view = createView(name, prefix, attrs);
                if (view != null) {
                    return view;
                }
            } catch (ClassNotFoundException e) {
                // In this case we want to let the base class take a crack
                // at it.
            }
        }

        return super.onCreateView(name, attrs);
    }

    public LayoutInflater cloneInContext(Context newContext) {
        return new PhoneLayoutInflater(this, newContext);
    }
}

可以看到PhoneLayoutInflater实现了onCreateView()方法，当调用LayoutInflater的inflate()时，最终就会调用onCreateView()，从而创建出view

public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {
    ......
    final View temp = createViewFromTag(root, name, inflaterContext, attrs);
    ......
}


View createViewFromTag(View parent, String name, Context context, AttributeSet attrs,
            boolean ignoreThemeAttr) {
    ......
    try {
        if (-1 == name.indexOf('.')) {
            view = onCreateView(parent, name, attrs);
        } else {
            view = createView(name, null, attrs);
        }
    } finally {
        mConstructorArgs[0] = lastContext;
    }
    ......
}

protected View onCreateView(String name, AttributeSet attrs)
         throws ClassNotFoundException {
     return createView(name, "android.view.", attrs);
}

二.LayoutParams

LayoutParams继承于Android.View.ViewGroup.LayoutParams,是ViewGroup的一个内部抽象类，封装了Layout的位置、高、宽等信息

LayoutParams类是用于child view(子视图)向parent view(父视图)传达自己的意愿的一个东西

ViewGroup.LayoutParams类只能简单的设置高height以及宽width两个基本的属性，宽和高都可以设置成三种值：

1，FILL_PARENT，一个确定的值；

2，MATCH_PARENT；

3，WRAP_CONTENT。

ViewGroup.MarginLayoutParams类是ViewGroup.LayoutParams的子类，顾名思义，它只能设置child View的margin属性信息。

1、利用setMargins(left,top,right,bottom);

2、利用MarginLayoutParams对象params方法单独设置.topMargin

基本使用：

常用子类的简单使用：LinearLayout.LayoutParams、RelativeLayout.Params以及WindowManager.Params。

例子：

            LayoutParams param = new LayoutParams(
                    0, LayoutParams.MATCH_PARENT);
            //param.gravity = Gravity.CENTER_VERTICAL;
            param.weight = 1;
            view.setLayoutParams(param);
            addView(view,i);