android TextView 容纳不下内容，让字向左滚动的办法

就是大家叫的跑马灯效果。对4.0以上，简单地在TextView里面加上4句就可以了： 

android:ellipsize="marquee"
android:focusable="true"
android:focusableInTouchMode="true"
android:singleLine="true"

但是如果这个TextView属于ListView的子View，并且list item设置了android:descendantFocusability="blocksDescendants"等比较复杂的情况时，上述方法不行。必须在自定义View上drawText，在http://gundumw100.iteye.com/blog/965366的基础上，整理了些干货：

FloatableTextView.java:

package com.example.floatabletextview;

import android.content.Context;
import android.graphics.Canvas;
import android.os.Parcel;
import android.os.Parcelable;
import android.util.AttributeSet;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.TextView;

/**
 * 单行TextView，容纳不下就左移
 */
public class FloatableTextView extends TextView implements OnClickListener {

    public boolean mIsFloating = false; //是否开始滚动
    private float mSpeed = 0.5f;
    private float mStep = 0f;
    private String mStr = ""; //文本内容
    private float mTextLength = 0f; //文本长度
    private float mViewWidth = 0f;
    private float mY = 0f; //文字的纵坐标


    public FloatableTextView(Context context) {
        super(context);
        initView();
    }

    public FloatableTextView(Context context, AttributeSet attrs) {
        super(context, attrs);
        initView();
    }

    public FloatableTextView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        initView();
    }


    private void initView() {
        setOnClickListener(this);
    }

    public void init(String str, float speed, float width) {
        setText(str);
        mSpeed = speed;
        mStr = getText().toString();
        mTextLength = getPaint().measureText(mStr);
        mViewWidth = width;
        mStep = mTextLength + mViewWidth;
        mY = getTextSize() + getPaddingTop();
        getPaint().setColor(0xff0000ff);
    }

    @Override
    public void onClick(View v) {
        if (mIsFloating)
            stopFloating();
        else
            startFloating();
    }

    @Override
    public void onDraw(Canvas canvas) {
        canvas.drawText(mStr, 0, mStr.length(), mViewWidth + mTextLength - mStep, mY, getPaint());
        if (!mIsFloating)
            return;
        mStep += mSpeed;
        if (mStep > mViewWidth + mTextLength * 2)
            mStep = mTextLength;
        invalidate();
    }

    @Override
    public void onRestoreInstanceState(Parcelable state) {
        if (!(state instanceof SavedState)) {
            super.onRestoreInstanceState(state);
            return;
        }
        SavedState savedState = (SavedState) state;
        super.onRestoreInstanceState(savedState.getSuperState());

        mStep = savedState.mStep;
        mIsFloating = savedState.mIsFloating;
    }

    @Override
    public Parcelable onSaveInstanceState() {
        Parcelable superState = super.onSaveInstanceState();
        SavedState savedState = new SavedState(superState);
        savedState.mStep = mStep;
        savedState.mIsFloating = mIsFloating;
        return savedState;
    }

    public void setSpeed(float speed) {
        mSpeed = speed;
    }

    public void startFloating() {
        mIsFloating = mTextLength > mViewWidth;
        // mIsFloating = true;
        invalidate();
    }

    public void stopFloating() {
        mIsFloating = false;
        invalidate();
    }

    public static class SavedState extends BaseSavedState {
        public static final Parcelable.Creator<SavedState> CREATOR = new Parcelable.Creator<SavedState>() {

            @Override
            public SavedState createFromParcel(Parcel in) {
                return new SavedState(in);
            }

            public SavedState[] newArray(int size) {
                return new SavedState[size];
            }
            
        };
        public boolean mIsFloating = false;
        public float mStep = 0.0f;

        private SavedState(Parcel in) {
            super(in);
            boolean[] b = new boolean[1];
            in.readBooleanArray(b);
            mIsFloating = b[0];
            mStep = in.readFloat();
        }

        SavedState(Parcelable superState) {
            super(superState);
        }

        @Override
        public void writeToParcel(Parcel out, int flags) {
            super.writeToParcel(out, flags);
            out.writeBooleanArray(new boolean[] {
                mIsFloating
            });
            out.writeFloat(mStep);
        }
    }

}

MainActivity.java:

package com.example.floatabletextview;

import android.app.ListActivity;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;

import com.example.zlistmarquee.R;

public class MainActivity extends ListActivity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        setListAdapter(new MyAdapter());
    }

    
    class MyAdapter extends BaseAdapter {

        @Override
        public int getCount() {
            return 9;
        }

        @Override
        public Object getItem(int position) {
            return null;
        }

        @Override
        public long getItemId(int position) {
            return 0;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            View v = getLayoutInflater().inflate(R.layout.list_item, null);
            FloatableTextView floatableTextView = (FloatableTextView) v.findViewById(R.id.floatable_text_view);
            floatableTextView.init("速度 岁的 电话 离开 的灯光 撒旦斯蒂芬 无污染", 0.9f, 100);
            floatableTextView.startFloating();
            return v;
        }
        
    }
    
}

list_item.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="30dp"
    android:orientation="horizontal" >

    <LinearLayout
        android:layout_width="90dp"
        android:layout_height="fill_parent"
        android:background="@android:color/holo_green_dark" >
    </LinearLayout>

    <com.example.floatabletextview.FloatableTextView
        android:id="@+id/floatable_text_view"
        android:layout_width="80dp"
        android:layout_height="30dp"
        android:background="@android:color/holo_blue_bright" />

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:background="@android:color/holo_green_light" >
    </LinearLayout>

</LinearLayout>

activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <ListView
        android:id="@android:id/list"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" >
    </ListView>

</LinearLayout>