引用

implementation 'com.github.bumptech.glide:glide:4.9.0'
annotationProcessor 'com.github.bumptech.glide:compiler:4.9.0'

使用

    Glide.with(GlideActivity.this)
                .load(url)
                .centerCrop()
                .placeholder(R.mipmap.ic_launcher)
                .error(R.mipmap.ic_launcher)
                .transform(new GlideCircleTransform(CommonStaffSelectedForRoleActivity.this))
                .into(imageView);

源码分析

主要方法glide绑定当前activity或者fragment生命周期，加载图片资源，设置图片展示scaleType，设置占位图，失败图，以及圆角设置等。

with

那么glide是怎样通过with传入的参数。如何绑定生命周期？如何传递生命周期？
首先从glide的静态方法with分析。

     @NonNull
    public static RequestManager with(@NonNull View view) {
    return getRetriever(view.getContext()).get(view);
    }
    @NonNull
    public static RequestManager with(@NonNull Context context) {
    return getRetriever(context).get(context);
    }
    @NonNull
    public static RequestManager with(@NonNull Activity activity) {
    return getRetriever(activity).get(activity);
      }
    @NonNull
    public static RequestManager with(@NonNull FragmentActivity activity) {
    return getRetriever(activity).get(activity);
    }
     @NonNull
    public static RequestManager with(@NonNull Fragment fragment) {
    return getRetriever(fragment.getActivity()).get(fragment);
    }

    @SuppressWarnings("deprecation")
    @Deprecated
    @NonNull
    public static RequestManager with(@NonNull android.app.Fragment fragment) {
    return getRetriever(fragment.getActivity()).get(fragment);
    }
    ……

参数可以是with的参数可以是android.app.Activity、android.app.Fragment、android.support.v4.app.Fragment、android.support.v4.app.FragmentActivity等。

    @NonNull
    private static RequestManagerRetriever getRetriever(@Nullable Context context) {
    // Context could be null for other reasons (ie the user passes in null), but in practice it will
    // only occur due to errors with the Fragment lifecycle.
    Preconditions.checkNotNull(
        context,
        "You cannot start a load on a not yet attached View or a Fragment where getActivity() "
            + "returns null (which usually occurs when getActivity() is called before the Fragment "
            + "is attached or after the Fragment is destroyed).");
    return Glide.get(context).getRequestManagerRetriever();
    }
内部都是通过getRetriever方法获取RequestManagerRetriever对象再调用get方法。

     @NonNull
    public RequestManager get(@NonNull FragmentActivity activity) {
    if (Util.isOnBackgroundThread()) {
      return get(activity.getApplicationContext());
    } else {
      assertNotDestroyed(activity);
      FragmentManager fm = activity.getSupportFragmentManager();
      return supportFragmentGet(
          activity, fm, /*parentHint=*/ null, isActivityVisible(activity));
    }
    }

    @NonNull
    public RequestManager get(@NonNull Fragment fragment) {
    Preconditions.checkNotNull(fragment.getActivity(),
          "You cannot start a load on a fragment before it is attached or after it is destroyed");
    if (Util.isOnBackgroundThread()) {
      return get(fragment.getActivity().getApplicationContext());
    } else {
      FragmentManager fm = fragment.getChildFragmentManager();
      return supportFragmentGet(fragment.getActivity(), fm, fragment, fragment.isVisible());
    }
    }

    @SuppressWarnings("deprecation")
    @NonNull
    public RequestManager get(@NonNull Activity activity) {
    if (Util.isOnBackgroundThread()) {
      return get(activity.getApplicationContext());
    } else {
      assertNotDestroyed(activity);
      android.app.FragmentManager fm = activity.getFragmentManager();
      return fragmentGet(
          activity, fm, /*parentHint=*/ null, isActivityVisible(activity));
    }
    }
    ……

通过get方法内部可以看出，通过将fm作为参数最后调用supportFragmentGet 或者fragmentGet返回一个RequestManager对象。那么这个RequestManager对象是干嘛的呢？接着下面看。

     @NonNull
    private RequestManager supportFragmentGet(
      @NonNull Context context,
      @NonNull FragmentManager fm,
      @Nullable Fragment parentHint,
      boolean isParentVisible) {
    SupportRequestManagerFragment current =
        getSupportRequestManagerFragment(fm, parentHint, isParentVisible);
    RequestManager requestManager = current.getRequestManager();
    if (requestManager == null) {
      // TODO(b/27524013): Factor out this Glide.get() call.
      Glide glide = Glide.get(context);
      requestManager =
          factory.build(
              glide, current.getGlideLifecycle(), current.getRequestManagerTreeNode(), context);
      current.setRequestManager(requestManager);
    }
    return requestManager;
    }
原来RequestManager是通过current（RequestManagerFragment）对setRequestManager设置的。首先看下getSupportRequestManagerFragment是怎么获取的RequestManagerFragment对象。

       @NonNull
    private SupportRequestManagerFragment getSupportRequestManagerFragment(
      @NonNull final FragmentManager fm, @Nullable Fragment parentHint, boolean isParentVisible) {
    SupportRequestManagerFragment current =
        (SupportRequestManagerFragment) fm.findFragmentByTag(FRAGMENT_TAG);
    if (current == null) {
      current = pendingSupportRequestManagerFragments.get(fm);
      if (current == null) {
        current = new SupportRequestManagerFragment();
        current.setParentFragmentHint(parentHint);
        if (isParentVisible) {
          current.getGlideLifecycle().onStart();
        }
        pendingSupportRequestManagerFragments.put(fm, current);
        fm.beginTransaction().add(current, FRAGMENT_TAG).commitAllowingStateLoss();
        handler.obtainMessage(ID_REMOVE_SUPPORT_FRAGMENT_MANAGER, fm).sendToTarget();
      }
    }
    return current;
    }

SupportRequestManagerFragment初始化的时候，需要创建一个ActivityFragmentLifecycle，初始化成员变量lifecycle。

    public SupportRequestManagerFragment() {
    this(new ActivityFragmentLifecycle());
    }

    @VisibleForTesting
    @SuppressLint("ValidFragment")
    public SupportRequestManagerFragment(@NonNull ActivityFragmentLifecycle lifecycle) {
    this.lifecycle = lifecycle;
    }

然后看到了下面这句

     fm.beginTransaction().add(current, FRAGMENT_TAG).commitAllowingStateLoss();

原来通过当前activity的fm管理器添加将空页面的SupportRequestManagerFragment的fragment添加进去，并返回这个空页面的fragment。

      if (requestManager == null) {
      // TODO(b/27524013): Factor out this Glide.get() call.
      Glide glide = Glide.get(context);
      requestManager =
          factory.build(
              glide, current.getGlideLifecycle(), current.getRequestManagerTreeNode(), context);
      current.setRequestManager(requestManager);
    }

再来看通过current.getLifecycle()获取fragment的lifecycle，传入requestManager，将fragment和requestManager建立联系。

load

load方法主要是加载网络地址，图片资源，可以是本地图片、应用资源、二进制流、uri对象。