如何让Android TextView在文本长度小于屏幕宽度时也能触发跑马灯滚动

Android 原生 TextView 跑马灯默认仅在文本宽度大于控件可用宽度时触发，要实现无论文本长短都持续滚动，需要自定义 TextView 改写触发逻辑。

1. 实现自定义跑马灯 TextView #

Kotlin 版本代码 #

class AlwaysMarqueeTextView @JvmOverloads constructor(
    context: Context,
    attrs: AttributeSet? = null,
    defStyleAttr: Int = android.R.attr.textViewStyle
) : AppCompatTextView(context, attrs, defStyleAttr) {

    init {
        ellipsize = TextUtils.TruncateAt.MARQUEE
        setSingleLine()
        marqueeRepeatLimit = -1
        isSelected = true
    }

    override fun isFocused(): Boolean {
        return true
    }

    override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec)
        val textWidth = paint.measureText(text.toString())
        val measuredWidth = measuredWidth
        if (textWidth < measuredWidth) {
            setMeasuredDimension(measuredWidth - 1, measuredHeight)
        }
    }

    override fun setText(text: CharSequence?, type: BufferType?) {
        super.setText(text, type)
        requestLayout()
    }
}

Java 版本代码 #

public class AlwaysMarqueeTextView extends AppCompatTextView {

    public AlwaysMarqueeTextView(Context context) {
        super(context);
        init();
    }

    public AlwaysMarqueeTextView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public AlwaysMarqueeTextView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    private void init() {
        setEllipsize(TextUtils.TruncateAt.MARQUEE);
        setSingleLine(true);
        setMarqueeRepeatLimit(-1);
        setSelected(true);
    }

    @Override
    public boolean isFocused() {
        return true;
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        float textWidth = getPaint().measureText(getText().toString());
        int measuredWidth = getMeasuredWidth();
        if (textWidth < measuredWidth) {
            setMeasuredDimension(measuredWidth - 1, getMeasuredHeight());
        }
    }

    @Override
    public void setText(CharSequence text, BufferType type) {
        super.setText(text, type);
        requestLayout();
    }
}

2. 替换布局中的原有控件 #

将XML中原来的TextView替换为自定义控件，注意修改com.your.packagename为你实际的类所在包路径：

<com.your.packagename.AlwaysMarqueeTextView
    android:id="@+id/tickler_message"
    style="@style/AppTheme.MarqueeTextStyle"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    tools:text="@string/placeholder_marquee_text"/>

3. 业务代码适配 #

原有Activity中的设置文本逻辑无需修改，isSelected配置可保留也可删除，自定义控件已经默认初始化了跑马灯所需的全部参数。

内容的提问来源于stack exchange，提问作者Sandeep Kumar