attachBaseContext的作用是什么? [英] What is the role of attachBaseContext?

问题描述

我对为什么在Android中使用attachBaseContext感到困惑.如果有人可以向我解释相同含义的话，那将是一个很大的帮助.

I am confused about why do we use attachBaseContext in android. It would be a great help if someone could explain to me the meaning for the same.

推荐答案

ContextWrapper类的attachBaseContext函数确保上下文仅被附加一次. ContextThemeWrapper应用来自应用程序或活动的主题，该主题在AndroidManifest.xml文件中定义为android:theme. 由于应用程序和服务都不需要主题，因此它们直接从ContextWrapper继承主题.在活动创建，应用程序和服务启动期间，每次都会创建一个新的ContextImpl对象，并在Context中实现功能.

The attachBaseContext function of the ContextWrapper class is making sure the context is attached only once. ContextThemeWrapper applies theme from application or Activity which is defined as android:theme in the AndroidManifest.xml file. Since both Application and Service do not need theme, they inherit it directly from ContextWrapper. During the activity creation, application and service are initiated, a new ContextImpl object is created each time and it implements functions in Context.

public class ContextWrapper extends Context {
    Context mBase;

    public ContextWrapper(Context base) {
        mBase = base;
    }

    /**
     * Set the base context for this ContextWrapper.  All calls will then be
     * delegated to the base context.  Throws
     * IllegalStateException if a base context has already been set.
     * 
     * @param base The new base context for this wrapper.
     */
    protected void attachBaseContext(Context base) {
        if (mBase != null) {
            throw new IllegalStateException("Base context already set");
        }
        mBase = base;
    }

}

有关更多详细信息，请参见此.

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