【android】ListView 的 transcriptMode 选项

悠悠 2022-07-13 14:55 162阅读 0赞

> 默认情况下，当添加的 Item 超出 ListView 的范围后，ListView 并没有刷新让最新一条显示出来。而在 qq/[微信][Link 1] 聊天中，发新的消息后会自动滚动显示出最下面的一条信息。

## 调用方式 ##

*  AbsListView.java：

public int getTranscriptMode()   // 用于查询当前的 transcript 模式
       
        
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void setTranscriptMode(int mode)   // 用于设置 transcript 模式
       
        
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AbsListView.TRANSCRIPT_MODE_DISABLED    // 禁用
        AbsListView.TRANSCRIPT_MODE_NORMAL   // 正常状态
        AbsListView.TRANSCRIPT_MODE_ALWAYS_SCROLL   // 总是滚动到最新一条
       
        
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## 布局文件设置 ##

<ListView android:id="@+id/lv_test"
            android:layout_width="match_parent"
            android:layout_height="300dp"
            
            android:transcriptMode="normal"
            android:transcriptMode="disabled"
            android:transcriptMode="alwaysScroll"
            >
       
        
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## 源码分析 ##

*  获取当前模式：

/** * Returns the current transcript mode. * * @return {@link #TRANSCRIPT_MODE_DISABLED}, {@link #TRANSCRIPT_MODE_NORMAL} or * {@link #TRANSCRIPT_MODE_ALWAYS_SCROLL} */
        public int getTranscriptMode() {
            return mTranscriptMode;
        }
       
        
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*  设置模式：

/** * Puts the list or grid into transcript mode. In this mode the list or grid will always scroll * to the bottom to show new items. * * @param mode the transcript mode to set * * @see #TRANSCRIPT_MODE_DISABLED * @see #TRANSCRIPT_MODE_NORMAL * @see #TRANSCRIPT_MODE_ALWAYS_SCROLL */
        public void setTranscriptMode(int mode) {
            mTranscriptMode = mode;
        }
       
        
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*  根据 mTranscriptMode 的值来对应设置 mLayoutMode 的状态：   
    
    
     *  如果是 TRANSCRIPT\_MODE\_ALWAYS\_SCROLL：则 强制 从 ListView 的底部开始刷新；
     *  如果是 TRANSCRIPT\_MODE\_NORMAL：如果当前的最后一个 Item 在 ListView 显示范围内，adapter 数据集内容变化时就从滚动底部；否则不滚动到底部！

@Override
        protected void handleDataChanged() {
            ... 省略 ...
                    if (mTranscriptMode == TRANSCRIPT_MODE_ALWAYS_SCROLL) {
                        mLayoutMode = LAYOUT_FORCE_BOTTOM;
                        return;
                    } else if (mTranscriptMode == TRANSCRIPT_MODE_NORMAL) {
                        if (mForceTranscriptScroll) {
                            mForceTranscriptScroll = false;
                            mLayoutMode = LAYOUT_FORCE_BOTTOM;
                            return;
                        }
                        final int childCount = getChildCount();
                        final int listBottom = getHeight() - getPaddingBottom();
                        final View lastChild = getChildAt(childCount - 1);
                        final int lastBottom = lastChild != null ? lastChild.getBottom() : listBottom;
                        if (mFirstPosition + childCount >= lastHandledItemCount &&
                                lastBottom <= listBottom) {
                            mLayoutMode = LAYOUT_FORCE_BOTTOM;
                            return;
                        }
                        // Something new came in and we didn't scroll; give the user a clue that
                        // there's something new.
                        awakenScrollBars();
                    }
            ... 省略 ...    
        }   
       
        
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@Override
        protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
            if (mSelector == null) {
                useDefaultSelector();
            }
            final Rect listPadding = mListPadding;
            listPadding.left = mSelectionLeftPadding + mPaddingLeft;
            listPadding.top = mSelectionTopPadding + mPaddingTop;
            listPadding.right = mSelectionRightPadding + mPaddingRight;
            listPadding.bottom = mSelectionBottomPadding + mPaddingBottom;
    
            // Check if our previous measured size was at a point where we should scroll later.
            if (mTranscriptMode == TRANSCRIPT_MODE_NORMAL) {
                final int childCount = getChildCount();
                final int listBottom = getHeight() - getPaddingBottom();
                final View lastChild = getChildAt(childCount - 1);
                final int lastBottom = lastChild != null ? lastChild.getBottom() : listBottom;
                mForceTranscriptScroll = mFirstPosition + childCount >= mLastHandledItemCount &&
                        lastBottom <= listBottom;
            }
        }
       
        
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## 实例 ##

*  test\_list\_view.xml：

<?xml version="1.0" encoding="utf-8"?>
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="match_parent" android:layout_height="match_parent">
    
        <ListView android:id="@+id/lv_test" android:layout_width="match_parent" android:layout_height="300dp" >
        </ListView>
        <Button android:id="@+id/btn_add_item" android:layout_width="match_parent" android:layout_height="40dp" android:text="增加新 item" />
        <Button android:id="@+id/btn_set_disable" android:layout_width="match_parent" android:layout_height="40dp" android:text="不滚动" />
        <Button android:id="@+id/btn_set_normal" android:layout_width="match_parent" android:layout_height="40dp" android:text="如果最后Item在显示范围内就滚动" />
        <Button android:id="@+id/btn_set_always" android:layout_width="match_parent" android:layout_height="40dp" android:text="总是滚动到最新一条" />
    
    </LinearLayout>
       
        
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*  MainActivity.java：

public class MainActivity extends Activity { 
    
        ArrayList<String> mItemStrArr = new ArrayList<>();
        ArrayAdapter mAdapter;
        int i = 0;
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.test_list_view);
    
            this.testListViewTranscriptMode();
        }
    
        void testListViewTranscriptMode(){
            Button btnAddItem = (Button) this.findViewById(R.id.btn_add_item);
    
            Button btnSetDisable = (Button) this.findViewById(R.id.btn_set_disable);
            Button btnSetNormal = (Button) this.findViewById(R.id.btn_set_normal);
            Button btnSetAlways = (Button) this.findViewById(R.id.btn_set_always);
    
            ListView lv = (ListView)this.findViewById(R.id.lv_test);
            // 实例化对象
            mAdapter = new ArrayAdapter(this, R.layout.test_item, R.id.tv_content, mItemStrArr);
            // 设置适配器
            lv.setAdapter(mAdapter);
            btnAddItem.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    mItemStrArr.add("item_" + i++);
                    mAdapter.notifyDataSetChanged();
                }
            });
            // 设置监听
            btnSetDisable.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    ListView lv = (ListView)MainActivity.this.findViewById(R.id.lv_test);
                    lv.setTranscriptMode(AbsListView.TRANSCRIPT_MODE_DISABLED);
                }
            });
            btnSetNormal.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    ListView lv = (ListView)MainActivity.this.findViewById(R.id.lv_test);
                    lv.setTranscriptMode(AbsListView.TRANSCRIPT_MODE_NORMAL);
                }
            });
            btnSetAlways.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    ListView lv = (ListView)MainActivity.this.findViewById(R.id.lv_test);
                    lv.setTranscriptMode(AbsListView.TRANSCRIPT_MODE_ALWAYS_SCROLL);
                }
            });
        }
       
        
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*  效果图：   
    
    
     *  disable 状态：   
        ![这里写图片描述][20160310210146306]
     *  normal 状态：   
        ![这里写图片描述][20160310210207057]
     *  always 状态：   
        ![这里写图片描述][20160310210223604]

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[Link 1]: http://lib.csdn.net/base/wechat
[20160310210146306]: /images/20220713/f1307e8250ee46179e5a7612a11567c7.png
[20160310210207057]: /images/20220713/408c91d28e9f454bb56c6d3d27ebfef3.png
[20160310210223604]: /images/20220713/92886f75861b4896bf2428e79ea7d2fc.png