TypedValue: 使用TypedValue将dip值转换成px值

之前自己一直手工编写函数来实现dip值到px值，今天无意中发现android本身就带有类似的函数来实现这种转换过程，就是 TypedValue.applyDimension

public class TypedValueApiUseDemoActivity extends AppCompatActivity {

    public static final String TAG = "xp.chen";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_typed_value_api_use_demo);

        int dipValue = 20;

        float density = getResources().getDisplayMetrics().density;
        int finalPx = (int) (dipValue * density);

        int pxValue = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dipValue, getResources().getDisplayMetrics());

        Log.i(TAG, "finalPx: "+finalPx+", pxValue: "+pxValue);

    }
}

Log:

I/xp.chen: finalPx: 60, pxValue: 60

查看下源码，android的实现和我们自己的实现是一样的：

/**
     * Converts an unpacked complex data value holding a dimension to its final floating
     * point value. The two parameters <var>unit</var> and <var>value</var>
     * are as in {@link #TYPE_DIMENSION}.
     *
     * @param unit The unit to convert from.
     * @param value The value to apply the unit to.
     * @param metrics Current display metrics to use in the conversion --
     *                supplies display density and scaling information.
     *
     * @return The complex floating point value multiplied by the appropriate
     * metrics depending on its unit.
     */
    public static float applyDimension(int unit, float value,
                                       DisplayMetrics metrics)
    {
        switch (unit) {
        case COMPLEX_UNIT_PX:
            return value;
        case COMPLEX_UNIT_DIP:
            return value * metrics.density;
        case COMPLEX_UNIT_SP:
            return value * metrics.scaledDensity;
        case COMPLEX_UNIT_PT:
            return value * metrics.xdpi * (1.0f/72);
        case COMPLEX_UNIT_IN:
            return value * metrics.xdpi;
        case COMPLEX_UNIT_MM:
            return value * metrics.xdpi * (1.0f/25.4f);
        }
        return 0;
    }