Android 各版本下设置Tablayout的宽度

1.在28.0之前

public void setIndicatorWidth(@NonNull final TabLayout tabLayout, final int margin) {
    tabLayout.post(new Runnable() {
        @Override
        public void run() {
            try {
                // 拿到tabLayout的mTabStrip属性
                Field mTabStripField = tabLayout.getClass().getDeclaredField("mTabStrip");
                mTabStripField.setAccessible(true);
                LinearLayout mTabStrip = (LinearLayout) mTabStripField.get(tabLayout);
                for (int i = 0; i < mTabStrip.getChildCount(); i++) {
                    View tabView = mTabStrip.getChildAt(i);
                    //拿到tabView的mTextView属性
                    Field mTextViewField = tabView.getClass().getDeclaredField("mTextView");
                    mTextViewField.setAccessible(true);
                    TextView mTextView = (TextView) mTextViewField.get(tabView);
                    tabView.setPadding(0, 0, 0, 0);
                    //因为我想要的效果是字多宽线就多宽，所以测量mTextView的宽度
                    int width = mTextView.getWidth();
                    if (width == 0) {
                        mTextView.measure(0, 0);
                        width = mTextView.getMeasuredWidth();
                    }
                    // 设置tab左右间距,注意这里不能使用Padding,因为源码中线的宽度是根据tabView的宽度来设置的
                    LinearLayout.LayoutParams params = (LinearLayout.LayoutParams) tabView.getLayoutParams();
                    params.width = width;
                    params.leftMargin = margin;
                    params.rightMargin = margin;
                    tabView.setLayoutParams(params);
                    tabView.invalidate();
                }
            } catch (NoSuchFieldException e) {
                e.printStackTrace();
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            }
        }
    });
}

2.在28.0版本

public void setIndicatorWidth(@NonNull final TabLayout tabLayout, final int margin) {
    tabLayout.post(new Runnable() {
        @Override
        public void run() {
            try {
                // 拿到tabLayout的slidingTabIndicator属性
                Field slidingTabIndicatorField = tabLayout.getClass().getDeclaredField("slidingTabIndicator");
                slidingTabIndicatorField.setAccessible(true);
                LinearLayout mTabStrip = (LinearLayout) slidingTabIndicatorField.get(tabLayout);
                for (int i = 0; i < mTabStrip.getChildCount(); i++) {
                    View tabView = mTabStrip.getChildAt(i);
                    //拿到tabView的mTextView属性
                    Field textViewField = tabView.getClass().getDeclaredField("textView");
                    textViewField.setAccessible(true);
                    TextView mTextView = (TextView) textViewField.get(tabView);
                    tabView.setPadding(0, 0, 0, 0);
                    // 因为想要的效果是字多宽线就多宽，所以测量mTextView的宽度
                    int width = mTextView.getWidth();
                    if (width == 0) {
                        mTextView.measure(0, 0);
                        width = mTextView.getMeasuredWidth();
                    }
                    // 设置tab左右间距,注意这里不能使用Padding,因为源码中线的宽度是根据tabView的宽度来设置的
                    LinearLayout.LayoutParams params = (LinearLayout.LayoutParams) tabView.getLayoutParams();
                    params.width = width;
                    params.leftMargin = margin;
                    params.rightMargin = margin;
                    tabView.setLayoutParams(params);
                    tabView.invalidate();
                }
            } catch (NoSuchFieldException e) {
                e.printStackTrace();
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            }
        }
    });
}

补充：如果只是为了宽度和字体宽度一样，tablayout已经加入了新属性

app:tabIndicatorFullWidth="false"

上面的方法可以设置固定宽度

如果28.0用以前的方法，会报错

java.lang.NullPointerException: Attempt to invoke virtual method 'void java.lang.reflect.Field.setAccessible(boolean)' on a null object reference

因为addTab的方法已经改变