Android RelativeLayout 讓 ImageView 寬度跟隨 TextView 文字寬度

問題現象

RelativeLayout 中有 TextView (標題) 和 ImageView (刪除線)，希望 ImageView 寬度**精確匹配** TextView 文字實際寬度，而非佔滿父容器。

錯誤代碼

    
    
    
    
        android:layout_height="match_parent"
        android:src="@drawable/strike_line" />

結果：title_container 寬度被 ImageView 撐滿，TextView 文字被截斷或置中不正確。

正確做法：ImageView 對齊 TextView 邊界

    
    
    
    
        android:layout_height="wrap_content"
        android:layout_centerVertical="true"
        android:layout_alignLeft="@id/title"          
        android:layout_alignRight="@id/title"         
        android:src="@drawable/strike_line"
        android:scaleType="fitXY" />                  

關鍵屬性解析

程式碼動態實現

RelativeLayout container = findViewById(R.id.title_container);
TextView title = findViewById(R.id.title);
ImageView strike = findViewById(R.id.title_strike_through);

// 確保參數為 RelativeLayout.LayoutParams
RelativeLayout.LayoutParams params = (RelativeLayout.LayoutParams) strike.getLayoutParams();
if (params == null) {
    params = new RelativeLayout.LayoutParams(
        ViewGroup.LayoutParams.WRAP_CONTENT,
        ViewGroup.LayoutParams.WRAP_CONTENT);
}
params.addRule(RelativeLayout.ALIGN_LEFT, title.getId());
params.addRule(RelativeLayout.ALIGN_RIGHT, title.getId());
params.addRule(RelativeLayout.CENTER_VERTICAL, RelativeLayout.TRUE);
strike.setLayoutParams(params);
strike.setScaleType(ImageView.ScaleType.FIT_XY);

進階：文字變動時自動調整 (TextWatcher)

title.addTextChangedListener(new TextWatcher() {
    @Override public void afterTextChanged(Editable s) {
        // 強制重新測量佈局，ImageView 會自動跟隨 TextView 新寬度
        title.requestLayout();
        strike.requestLayout();
    }
    @Override public void beforeTextChanged(CharSequence s, int start, int count, int after) {}
    @Override public void onTextChanged(CharSequence s, int start, int before, int count) {}
});

替代方案：自訂 View 繪製刪除線 (更輕量)

public class StrikeThroughTextView extends TextView {
    private Paint strikePaint;
    
    public StrikeThroughTextView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }
    
    private void init() {
        strikePaint = new Paint();
        strikePaint.setColor(Color.RED);
        strikePaint.setStrokeWidth(3f);
        strikePaint.setAntiAlias(true);
    }
    
    @Override protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        // 計算文字基線位置
        float y = getBaseline() - getTextSize() / 3; // 刪除線大概位置
        canvas.drawLine(0, y, getMeasuredWidth(), y, strikePaint);
    }
}

優勢：無額外 View、自動匹配文字寬度、效能更好、支援動畫。