Android應用層（View體系）三

自定義View

繼承系統控件的自定義View

這種自定義View在系統控件的基礎上進行拓展，一般是添加新的功能或者修改顯示的效果，一般情況下我們在onDraw()方法中進行處理

Step 1 : InvalidTextView.java

public class InvalidTextView extends TextView {
    private Paint mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    public InvalidTextView(Context context) {
        super(context);
        initDraw();
    }
    public InvalidTextView(Context context, AttributeSet attrs) {
        super(context, attrs);
        initDraw();
    }
    public InvalidTextView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        initDraw();
    }
    private void initDraw() {
        mPaint.setColor(Color.RED);
        mPaint.setStrokeWidth((float) 1.5);
    }
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        int width = getWidth();
        int height = getHeight();
        canvas.drawLine(0, height / 2, width, height / 2, mPaint);
    }
}

Step 2 ：XML中引用自定義View

<com.example.liuwangshu.mooncustomview.InvalidTextView
    android:id="@+id/iv_text"
    android:layout_width="200dp"
    android:layout_height="100dp"
    android:background="@android:color/holo_blue_light"
    android:gravity="center"
    android:textSize="16sp"
    android:layout_centerHorizontal="true"
    />

繼承View的自定義View

Step 1 : RectView.java

public class RectView extends View {
    private Paint mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    private int mColor=Color.RED;
    public RectView(Context context) {
        super(context);
        initDraw();
    }
    public RectView(Context context, AttributeSet attrs) {
        super(context, attrs);
        initDraw();
    }
    public RectView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        initDraw();
    }
    private void initDraw() {
        mPaint.setColor(mColor);
        mPaint.setStrokeWidth((float) 1.5);
    }
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        int width = getWidth();
        int height = getHeight();
        canvas.drawRect(0, 0, width, height, mPaint);
    }
}

Step 2 : 佈局中引用RectView

<com.example.liuwangshu.mooncustomview.RectView
      android:id="@+id/rv_rect"
      android:layout_width="200dp"
      android:layout_height="200dp"
      android:layout_below="@id/iv_text"
      android:layout_marginTop="50dp"
      android:layout_centerHorizontal="true"/>

Step 3 : 對padding屬性進行處理

如果我在佈局文件中設置pading屬性，發現沒有任何的作用，看來還得對padding屬性進行處理，只需要在onDraw()方法中稍加修改就可以了，在繪製正方形的時候考慮到padding屬性就可以了：

@Override
   protected void onDraw(Canvas canvas) {
       super.onDraw(canvas);
       int paddingLeft=getPaddingLeft();
       int paddingRight=getPaddingRight();
       int paddingTop=getPaddingTop();
       int paddingBottom=getPaddingBottom();
       int width = getWidth()-paddingLeft-paddingRight;
       int height = getHeight()-paddingTop-paddingBottom;
       canvas.drawRect(0+paddingLeft, 0+paddingTop, width+paddingRight, height+paddingBottom, mPaint);
   }

修改佈局文件加入padding屬性：

<com.example.liuwangshu.mooncustomview.RectView
    android:id="@+id/rv_rect"
    android:layout_width="200dp"
    android:layout_height="200dp"
    android:layout_below="@id/iv_text"
    android:layout_marginTop="50dp"
    android:layout_centerHorizontal="true"
    android:padding="10dp"/>

Step 4 : 對wrap_content屬性進行處理

在onMeasure()方法中指定一個默認的寬和高，在設置wrap_content屬性時設置此默認的寬和高就可以了：

@Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
      super.onMeasure(widthMeasureSpec, heightMeasureSpec);
      int widthSpecMode = MeasureSpec.getMode(widthMeasureSpec);
      int heightSpecMode = MeasureSpec.getMode(heightMeasureSpec);
      int widthSpecSize=MeasureSpec.getSize(widthMeasureSpec);
      int heightSpecSize=MeasureSpec.getSize(heightMeasureSpec);
      if(widthSpecMode==MeasureSpec.AT_MOST&&heightSpecMode==MeasureSpec.AT_MOST){
          setMeasuredDimension(400,400);
      }else if(widthSpecMode==MeasureSpec.AT_MOST){
          setMeasuredDimension(400,heightSpecSize);
      }else if(heightSpecMode==MeasureSpec.AT_MOST){
          setMeasuredDimension(widthSpecSize,400);
      }
  }

Step 5 : 自定義屬性

自定義view的完整代碼

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;
public class RectView extends View {
    private Paint mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    private int mColor=Color.RED;
    public RectView(Context context) {
        super(context);
        initDraw();
    }
    public RectView(Context context, AttributeSet attrs) {
        super(context, attrs);
        TypedArray mTypedArray=context.obtainStyledAttributes(attrs,R.styleable.RectView);
        //提取RectView屬性集合的rect_color屬性，如果沒設置默認值爲Color.RED
        mColor=mTypedArray.getColor(R.styleable.RectView_rect_color,Color.RED);
        //獲取資源後要及時回收
        mTypedArray.recycle();
        initDraw();
    }
    public RectView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        initDraw();
    }
    private void initDraw() {
        mPaint.setColor(mColor);
        mPaint.setStrokeWidth((float) 1.5);
    }
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        int widthSpecMode = MeasureSpec.getMode(widthMeasureSpec);
        int heightSpecMode = MeasureSpec.getMode(heightMeasureSpec);
        int widthSpecSize=MeasureSpec.getSize(widthMeasureSpec);
        int heightSpecSize=MeasureSpec.getSize(heightMeasureSpec);
        if(widthSpecMode==MeasureSpec.AT_MOST&&heightSpecMode==MeasureSpec.AT_MOST){
            setMeasuredDimension(400,400);
        }else if(widthSpecMode==MeasureSpec.AT_MOST){
            setMeasuredDimension(400,heightSpecSize);
        }else if(heightSpecMode==MeasureSpec.AT_MOST){
            setMeasuredDimension(widthSpecSize,400);
        }
    }
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        int paddingLeft = getPaddingLeft();
        int paddingRight = getPaddingRight();
        int paddingTop = getPaddingTop();
        int paddingBottom = getPaddingBottom();
        int width = getWidth() - paddingLeft - paddingRight;
        int height = getHeight() - paddingTop - paddingBottom;
        canvas.drawRect(0 + paddingLeft, 0 + paddingTop, width + paddingRight, height + paddingBottom, mPaint);
    }
}