获取Context对象

通常方法：

private static Context mContext; 
 public static Context getContext() {
       return mContext;
}
    @Override
    public void onCreate() {
        super.onCreate();
        mContext = this.getApplicationContext();
    }

我们会直接在Application中写一个static Context然后再onCreate赋值，由于Application在程序运行中只onCreate一次且伴随程序的生命周期，所以没很大问题的。
但是如果我们要随时的使用伴随Activity生命周期的Context怎么办呢。
这里我们采用WeakReference来一直持有当前显示页的Context。
在BaseActivity中去更新Application 中 保存Context的WeakReference，使其一直保存着显示页的Context。
话不多说直接上代码：
BaseApplication：

import android.annotation.SuppressLint;
import android.app.Application;
import android.content.Context;
import android.content.res.Configuration;

import java.lang.ref.WeakReference;

/**
 * Created by 奈蜇 on 2018-11-01.
 * BaseApplication
 */
public abstract class BaseApplication extends Application {
    private String TAG;

    @SuppressLint("StaticFieldLeak")
    private static Context mContext;
    private volatile static WeakReference<Context> mContextWeakReference = null;

    public static Context getContext() {
        if (mContextWeakReference == null || mContextWeakReference.get() == null) {
           synchronized (BaseApplication.class){
               if(mContextWeakReference == null || mContextWeakReference.get() == null){
                   mContextWeakReference = new WeakReference<>(mContext);
               }
           }
        }
        return mContextWeakReference.get();
    }
    public static void setContextRef(Context contextRef){
        mContextWeakReference = new WeakReference<>(contextRef);
    }


    @Override
    public void onCreate() {
        TAG = this.getClass().getName();
        LOG.D(TAG,"onCreate:" + this.toString());
        super.onCreate();
        mContext = this.getApplicationContext();
    }

    /**
     * 在开程序在内核中结束的时候执行,退出程序不一定会执行.
     */
    @Override
    public void onTerminate() {
        LOG.D(TAG,"onTerminate:" + this.toString());
        TAG = null;
        super.onTerminate();
    }

    /**
     * 配置改变时触发这个方法,例如屏幕方向切换.
     */
    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
    }

    /**
     * 内存匮乏时会调用.
     */
    @Override
    public void onLowMemory() {
        super.onLowMemory();
    }

    /**
     * 每次计算进程优先级满足条件时会调用,回调不同的内存状态.
     */
    @Override
    public void onTrimMemory(int level) {
        super.onTrimMemory(level);
    }
}

BaseActivity:

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;

/**
 * Created by 奈蜇 on 2018-11-01.
 *  基础活动类
 */
public abstract class BaseActivity extends AppCompatActivity {
    private String TAG;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        TAG = this.getClass().getName();
        LOG.D(TAG, "onCreate:  " + this.toString());
        super.onCreate(savedInstanceState);
        BaseApplication.setContextRef(this);
    }

    @Override
    protected void onStart() {
        LOG.D(TAG, "onStart:  " + this.toString());
        super.onStart();
    }

    @Override
    protected void onResume() {
        LOG.D(TAG, "onResume:  " + this.toString());
        super.onResume();
        BaseApplication.setContextRef(this);//保证弱引用一直引用当前的可见页面
    }

    @Override
    protected void onPause() {
        LOG.D(TAG, "onPause:  " + this.toString());
        super.onPause();
    }

    @Override
    protected void onStop() {
        LOG.D(TAG, "onStop:  " + this.toString());
        super.onStop();
    }

    @Override
    protected void onRestart() {
        LOG.D(TAG, "onRestart:  " + this.toString());
        super.onRestart();
    }

    @Override
    protected void onDestroy() {
        LOG.D(TAG, "onDestroy:  " + this.toString());
        TAG = null;
        super.onDestroy();
    }
}