android中ZoomControls 源码解析

解析

ZoomControls位于android.widget包下，是一个自定义的LinearLayout。里面有两个ZoomButton，一个zoomIn和一个zoomOut，并且为这两个按钮提供了设置监听器的接口，还有一些其他接口，比如设置缩放的速度、显示和隐藏（带动画效果）、设置内置缩放控件是否可用、重写了View的hasFocus()方法定义自己的焦点判断为其zoomIn或者zoomOut是否有焦点。

源码

/*
 * Copyright (C) 2008 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.widget;

import android.annotation.Widget;
import android.content.Context;
import android.util.AttributeSet;
import android.view.LayoutInflater;
import android.view.MotionEvent;
import android.view.View;
import android.view.accessibility.AccessibilityEvent;
import android.view.accessibility.AccessibilityNodeInfo;
import android.view.animation.AlphaAnimation;

import com.android.internal.R;


/**
 * The {@code ZoomControls} class displays a simple set of controls used for zooming and
 * provides callbacks to register for events. */
@Widget
public class ZoomControls extends LinearLayout {

    private final ZoomButton mZoomIn;
    private final ZoomButton mZoomOut;
        
    public ZoomControls(Context context) {
        this(context, null);
    }

    public ZoomControls(Context context, AttributeSet attrs) {
        super(context, attrs);
        setFocusable(false);
        
        LayoutInflater inflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        inflater.inflate(R.layout.zoom_controls, this, // we are the parent
                true);
        
        mZoomIn = (ZoomButton) findViewById(R.id.zoomIn);
        mZoomOut = (ZoomButton) findViewById(R.id.zoomOut);
    }

    public void setOnZoomInClickListener(OnClickListener listener) {
        mZoomIn.setOnClickListener(listener);
    }
    
    public void setOnZoomOutClickListener(OnClickListener listener) {
        mZoomOut.setOnClickListener(listener);
    }
    
    /*
     * Sets how fast you get zoom events when the user holds down the
     * zoom in/out buttons.
     */
    public void setZoomSpeed(long speed) {
        mZoomIn.setZoomSpeed(speed);
        mZoomOut.setZoomSpeed(speed);
    }
    
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        
        /* Consume all touch events so they don't get dispatched to the view
         * beneath this view.
         */
        return true;
    }
    
    public void show() {
        fade(View.VISIBLE, 0.0f, 1.0f);
    }
    
    public void hide() {
        fade(View.GONE, 1.0f, 0.0f);
    }
    
    private void fade(int visibility, float startAlpha, float endAlpha) {
        AlphaAnimation anim = new AlphaAnimation(startAlpha, endAlpha);
        anim.setDuration(500);
        startAnimation(anim);
        setVisibility(visibility);
    }
    
    public void setIsZoomInEnabled(boolean isEnabled) {
        mZoomIn.setEnabled(isEnabled);
    }
    
    public void setIsZoomOutEnabled(boolean isEnabled) {
        mZoomOut.setEnabled(isEnabled);
    }
    
    @Override
    public boolean hasFocus() {
        return mZoomIn.hasFocus() || mZoomOut.hasFocus();
    }

    @Override
    public void onInitializeAccessibilityEvent(AccessibilityEvent event) {
        super.onInitializeAccessibilityEvent(event);
        event.setClassName(ZoomControls.class.getName());
    }

    @Override
    public void onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo info) {
        super.onInitializeAccessibilityNodeInfo(info);
        info.setClassName(ZoomControls.class.getName());
    }
}