欢迎您访问程序员文章站本站旨在为大家提供分享程序员计算机编程知识!
您现在的位置是: 首页  >  IT编程

自定义view哪个构造方法是不能不重写的

程序员文章站 2022-03-02 17:28:43
在setContentView源码可以看到普通view的创建方法是createViewFromTag。找到view = createView(context, name, null, attrs);点进去看到根节点的view是通过反射获取的,然后获取根节点的构造方法clazz.getConstructor(mConstructorSignature)mConstructorSignature是两个参数的数组。所以自定义View一定要重写两个参数的构造函数/*** Creates a view fr...

在setContentView源码可以看到普通view的创建方法是createViewFromTag。
找到view = createView(context, name, null, attrs);
点进去看到根节点的view是通过反射获取的,然后获取根节点的构造方法clazz.getConstructor(mConstructorSignature)
mConstructorSignature是两个参数的数组。所以自定义View一定要重写两个参数的构造函数

/**
     * Creates a view from a tag name using the supplied attribute set.
     * <p>
     * <strong>Note:</strong> Default visibility so the BridgeInflater can
     * override it.
     *
     * @param parent the parent view, used to inflate layout params
     * @param name the name of the XML tag used to define the view
     * @param context the inflation context for the view, typically the
     *                {@code parent} or base layout inflater context
     * @param attrs the attribute set for the XML tag used to define the view
     * @param ignoreThemeAttr {@code true} to ignore the {@code android:theme}
     *                        attribute (if set) for the view being inflated,
     *                        {@code false} otherwise
     */
    @UnsupportedAppUsage
    View createViewFromTag(View parent, String name, Context context, AttributeSet attrs,
            boolean ignoreThemeAttr) {
        if (name.equals("view")) {
            name = attrs.getAttributeValue(null, "class");
        }

        // Apply a theme wrapper, if allowed and one is specified.
        if (!ignoreThemeAttr) {
            final TypedArray ta = context.obtainStyledAttributes(attrs, ATTRS_THEME);
            final int themeResId = ta.getResourceId(0, 0);
            if (themeResId != 0) {
                context = new ContextThemeWrapper(context, themeResId);
            }
            ta.recycle();
        }

        try {
            View view = tryCreateView(parent, name, context, attrs);

            if (view == null) {
                final Object lastContext = mConstructorArgs[0];
                mConstructorArgs[0] = context;
                try {
                    if (-1 == name.indexOf('.')) {
                        view = onCreateView(context, parent, name, attrs);
                    } else {
                        view = createView(context, name, null, attrs);
                    }
                } finally {
                    mConstructorArgs[0] = lastContext;
                }
            }

            return view;
        } catch (InflateException e) {
            throw e;

        } catch (ClassNotFoundException e) {
            final InflateException ie = new InflateException(
                    getParserStateDescription(context, attrs)
                    + ": Error inflating class " + name, e);
            ie.setStackTrace(EMPTY_STACK_TRACE);
            throw ie;

        } catch (Exception e) {
            final InflateException ie = new InflateException(
                    getParserStateDescription(context, attrs)
                    + ": Error inflating class " + name, e);
            ie.setStackTrace(EMPTY_STACK_TRACE);
            throw ie;
        }
    }

 /**
     * Low-level function for instantiating a view by name. This attempts to
     * instantiate a view class of the given <var>name</var> found in this
     * LayoutInflater's ClassLoader.
     *
     * <p>
     * There are two things that can happen in an error case: either the
     * exception describing the error will be thrown, or a null will be
     * returned. You must deal with both possibilities -- the former will happen
     * the first time createView() is called for a class of a particular name,
     * the latter every time there-after for that class name.
     *
     * @param viewContext The context used as the context parameter of the View constructor
     * @param name The full name of the class to be instantiated.
     * @param attrs The XML attributes supplied for this instance.
     *
     * @return View The newly instantiated view, or null.
     */
    @Nullable
    public final View createView(@NonNull Context viewContext, @NonNull String name,
            @Nullable String prefix, @Nullable AttributeSet attrs)
            throws ClassNotFoundException, InflateException {
        Objects.requireNonNull(viewContext);
        Objects.requireNonNull(name);
        Constructor<? extends View> constructor = sConstructorMap.get(name);
        if (constructor != null && !verifyClassLoader(constructor)) {
            constructor = null;
            sConstructorMap.remove(name);
        }
        Class<? extends View> clazz = null;

        try {
            Trace.traceBegin(Trace.TRACE_TAG_VIEW, name);

            if (constructor == null) {
                // Class not found in the cache, see if it's real, and try to add it
                clazz = Class.forName(prefix != null ? (prefix + name) : name, false,
                        mContext.getClassLoader()).asSubclass(View.class);

                if (mFilter != null && clazz != null) {
                    boolean allowed = mFilter.onLoadClass(clazz);
                    if (!allowed) {
                        failNotAllowed(name, prefix, viewContext, attrs);
                    }
                }
                constructor = clazz.getConstructor(mConstructorSignature);
                constructor.setAccessible(true);
                sConstructorMap.put(name, constructor);
            } else {
                // If we have a filter, apply it to cached constructor
                if (mFilter != null) {
                    // Have we seen this name before?
                    Boolean allowedState = mFilterMap.get(name);
                    if (allowedState == null) {
                        // New class -- remember whether it is allowed
                        clazz = Class.forName(prefix != null ? (prefix + name) : name, false,
                                mContext.getClassLoader()).asSubclass(View.class);

                        boolean allowed = clazz != null && mFilter.onLoadClass(clazz);
                        mFilterMap.put(name, allowed);
                        if (!allowed) {
                            failNotAllowed(name, prefix, viewContext, attrs);
                        }
                    } else if (allowedState.equals(Boolean.FALSE)) {
                        failNotAllowed(name, prefix, viewContext, attrs);
                    }
                }
            }

            Object lastContext = mConstructorArgs[0];
            mConstructorArgs[0] = viewContext;
            Object[] args = mConstructorArgs;
            args[1] = attrs;

            try {
                final View view = constructor.newInstance(args);
                if (view instanceof ViewStub) {
                    // Use the same context when inflating ViewStub later.
                    final ViewStub viewStub = (ViewStub) view;
                    viewStub.setLayoutInflater(cloneInContext((Context) args[0]));
                }
                return view;
            } finally {
                mConstructorArgs[0] = lastContext;
            }
        } catch (NoSuchMethodException e) {
            final InflateException ie = new InflateException(
                    getParserStateDescription(viewContext, attrs)
                    + ": Error inflating class " + (prefix != null ? (prefix + name) : name), e);
            ie.setStackTrace(EMPTY_STACK_TRACE);
            throw ie;

        } catch (ClassCastException e) {
            // If loaded class is not a View subclass
            final InflateException ie = new InflateException(
                    getParserStateDescription(viewContext, attrs)
                    + ": Class is not a View " + (prefix != null ? (prefix + name) : name), e);
            ie.setStackTrace(EMPTY_STACK_TRACE);
            throw ie;
        } catch (ClassNotFoundException e) {
            // If loadClass fails, we should propagate the exception.
            throw e;
        } catch (Exception e) {
            final InflateException ie = new InflateException(
                    getParserStateDescription(viewContext, attrs) + ": Error inflating class "
                            + (clazz == null ? "<unknown>" : clazz.getName()), e);
            ie.setStackTrace(EMPTY_STACK_TRACE);
            throw ie;
        } finally {
            Trace.traceEnd(Trace.TRACE_TAG_VIEW);
        }
    }
    ```

本文地址:https://blog.csdn.net/weixin_37165769/article/details/110958333

相关标签: problem android