Android ViewStub控件使用

ViewStub是android中view的一种优化方案，它的目的是在不需要显示view的时候不去加载view，这样在view的创建时期，减少了加载的资源，优化了view。

下面就用代码来说明如何使用viewstub。

先上图

功能很简单，当点击traggle时，下面的viewstub会加载其中预置的layout，再次点击时，隐藏viewstub。

代码如下

activity_main.xml

    
    text_layout" />
    

text_layout.xml

Main_Activity.java

package com.example.listscroll;

import android.app.Activity;
import android.app.ListActivity;
import android.content.Context;
import android.os.Bundle;
import android.os.Handler;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.view.ViewStub;
import android.view.WindowManager;
import android.view.animation.AnimationUtils;
import android.widget.AbsListView;
import android.widget.BaseAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.TextView;

public class MainActivity extends Activity {

	private boolean mShowed;
	private View mTextPanel;
	
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		Button btn = (Button) findViewById(R.id.btn);
		btn.setOnClickListener(new OnClickListener() {
			
			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				if (mTextPanel == null) {
					mTextPanel = ((ViewStub) findViewById(R.id.stub)).inflate();
				}
				if (mShowed == false) {
					mShowed = true;
					showPanel(mTextPanel, true);
				} else {
					mShowed = false;
					hidePanel(mTextPanel, true);
				}
			}
		});
	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		// Inflate the menu; this adds items to the action bar if it is present.
		getMenuInflater().inflate(R.menu.main, menu);
		return true;
	}
	
    private void showPanel(View panel, boolean slideUp) {
        panel.startAnimation(AnimationUtils.loadAnimation(this,
                slideUp ? R.anim.slide_in : R.anim.slide_out_top));
        panel.setVisibility(View.VISIBLE);
    }

    private void hidePanel(View panel, boolean slideDown) {
        panel.startAnimation(AnimationUtils.loadAnimation(this,
                slideDown ? R.anim.slide_out : R.anim.slide_in_top));
        panel.setVisibility(View.GONE);
    }
}

下面是4个简单的动画效果，展示viewstub的加载

slide_in_top.xml

slide_in.xml

slide_out_top.xml

slide_out.xml

ViewStub中加载layout的代码是

    public View inflate() {
        final ViewParent viewParent = getParent();// 获取当前view的父view，用于获取需要加载的layout的index

        if (viewParent != null && viewParent instanceof ViewGroup) {
            if (mLayoutResource != 0) {
                final ViewGroup parent = (ViewGroup) viewParent;
                final LayoutInflater factory;
                if (mInflater != null) {
                    factory = mInflater;
                } else {
                    factory = LayoutInflater.from(mContext);
                }
                final View view = factory.inflate(mLayoutResource, parent, false);// 获取需要加载的layout

                if (mInflatedId != NO_ID) {
                    view.setId(mInflatedId);
                }

                final int index = parent.indexOfChild(this);
                parent.removeViewInLayout(this);// 删除之前加载的view

                final ViewGroup.LayoutParams layoutParams = getLayoutParams();
                if (layoutParams != null) {
                    parent.addView(view, index, layoutParams);
                } else {
                    parent.addView(view, index);// 添加view
                }

                mInflatedViewRef = new WeakReference(view);

                if (mInflateListener != null) {
                    mInflateListener.onInflate(this, view);
                }

                return view;
            } else {
                throw new IllegalArgumentException("ViewStub must have a valid layoutResource");
            }
        } else {
            throw new IllegalStateException("ViewStub must have a non-null ViewGroup viewParent");
        }
    }