沒有默認的構造函數

Question

我不斷收到錯誤消息，導致程序崩潰。

“ com.example.AutoResizeTextClock.AutoResizeTextClock沒有默認構造函數”

我假設它是我的AndroidManifest.XML中的android：name，但是我不知道問題出在哪里。 任何幫助，將不勝感激！

AndroidManifest.XML

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.android.AutoResizeTextClock" >

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme" >
    <activity
        android:name=".AutoResizeTextClock"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
</application>

</manifest>

activity_auto_resize_text_view.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical"
android:padding="32dp"
android:background="#ff000000">

<com.example.android.clocktest.AutoResizeTextClock
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:ellipsize="none"
    android:gravity="center"
    android:maxLines="1"
    android:text="Auto Resized Text, max 1 line"
    android:textSize="500sp"
    android:textColor="#fff44336"
    android:textFont=""
    /> <!-- maximum size -->


</LinearLayout>

AutoResizeTextClock.java

package com.example.android.clocktest;
import android.annotation.TargetApi;
import android.content.Context;
import android.content.res.Resources;
import android.graphics.RectF;
import android.os.Build;
import android.text.Layout.Alignment;
import android.text.StaticLayout;
import android.text.TextPaint;
import android.util.AttributeSet;
import android.util.SparseIntArray;
import android.util.TypedValue;
import android.widget.TextClock;


public class AutoResizeTextClock extends TextClock {
    private interface SizeTester {
        /**
         *
         * @param suggestedSize
         *            Size of text to be tested
         * @param availableSpace
         *            available space in which text must fit
         * @return an integer < 0 if after applying {@code suggestedSize} to
         *         text, it takes less space than {@code availableSpace}, > 0
         *         otherwise
         */
        public int onTestSize(int suggestedSize, RectF availableSpace);
    }

    private RectF mTextRect = new RectF();

    private RectF mAvailableSpaceRect;

    private SparseIntArray mTextCachedSizes;

    private TextPaint mPaint;

    private float mMaxTextSize;

    private float mSpacingMult = 1.0f;

    private float mSpacingAdd = 0.0f;

    private float mMinTextSize = 20;

    private int mWidthLimit;

    private static final int NO_LINE_LIMIT = -1;
    private int mMaxLines;

    private boolean mEnableSizeCache = true;
    private boolean mInitiallized;

    public AutoResizeTextClock(Context context) {
        super(context);
        initialize();
    }

    public AutoResizeTextClock(Context context, AttributeSet attrs) {
        super(context, attrs);
        initialize();
    }

    public AutoResizeTextClock(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        initialize();
    }

    private void initialize() {
        mPaint = new TextPaint(getPaint());
        mMaxTextSize = getTextSize();
        mAvailableSpaceRect = new RectF();
        mTextCachedSizes = new SparseIntArray();
        if (mMaxLines == 0) {
            // no value was assigned during construction
            mMaxLines = NO_LINE_LIMIT;
        }
        mInitiallized = true;
    }

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

    @Override
    public void setTextSize(float size) {
        mMaxTextSize = size;
        mTextCachedSizes.clear();
        adjustTextSize(getText().toString());
    }

    @Override
    public void setMaxLines(int maxlines) {
        super.setMaxLines(maxlines);
        mMaxLines = maxlines;
        reAdjust();
    }

    public int getMaxLines() {
        return mMaxLines;
    }

    @Override
    public void setSingleLine() {
        super.setSingleLine();
        mMaxLines = 1;
        reAdjust();
    }

    @Override
    public void setSingleLine(boolean singleLine) {
        super.setSingleLine(singleLine);
        if (singleLine) {
            mMaxLines = 1;
        } else {
            mMaxLines = NO_LINE_LIMIT;
        }
        reAdjust();
    }

    @Override
    public void setLines(int lines) {
        super.setLines(lines);
        mMaxLines = lines;
        reAdjust();
    }

    @Override
    public void setTextSize(int unit, float size) {
        Context c = getContext();
        Resources r;

        if (c == null)
            r = Resources.getSystem();
        else
            r = c.getResources();
        mMaxTextSize = TypedValue.applyDimension(unit, size,
                r.getDisplayMetrics());
        mTextCachedSizes.clear();
        adjustTextSize(getText().toString());
    }

    @Override
    public void setLineSpacing(float add, float mult) {
        super.setLineSpacing(add, mult);
        mSpacingMult = mult;
        mSpacingAdd = add;
    }

    /**
     * Set the lower text size limit and invalidate the view
     *
     * @param minTextSize
     */
    public void setMinTextSize(float minTextSize) {
        mMinTextSize = minTextSize;
        reAdjust();
    }

    private void reAdjust() {
        adjustTextSize(getText().toString());
    }

    private void adjustTextSize(String string) {
        if (!mInitiallized) {
            return;
        }
        int startSize = (int) mMinTextSize;
        int heightLimit = getMeasuredHeight() - getCompoundPaddingBottom()
                - getCompoundPaddingTop();
        mWidthLimit = getMeasuredWidth() - getCompoundPaddingLeft()
                - getCompoundPaddingRight();
        mAvailableSpaceRect.right = mWidthLimit;
        mAvailableSpaceRect.bottom = heightLimit;
        super.setTextSize(
                TypedValue.COMPLEX_UNIT_PX,
                efficientTextSizeSearch(startSize, (int) mMaxTextSize,
                        mSizeTester, mAvailableSpaceRect));
    }

    private final SizeTester mSizeTester = new SizeTester() {
        @TargetApi(Build.VERSION_CODES.JELLY_BEAN)
        @Override
        public int onTestSize(int suggestedSize, RectF availableSPace) {
            mPaint.setTextSize(suggestedSize);
            String text = getText().toString();
            boolean singleline = getMaxLines() == 1;
            if (singleline) {
                mTextRect.bottom = mPaint.getFontSpacing();
                mTextRect.right = mPaint.measureText(text);
            } else {
                StaticLayout layout = new StaticLayout(text, mPaint,
                        mWidthLimit, Alignment.ALIGN_NORMAL, mSpacingMult,
                        mSpacingAdd, true);
                // return early if we have more lines
                if (getMaxLines() != NO_LINE_LIMIT
                        && layout.getLineCount() > getMaxLines()) {
                    return 1;
                }
                mTextRect.bottom = layout.getHeight();
                int maxWidth = -1;
                for (int i = 0; i < layout.getLineCount(); i++) {
                    if (maxWidth < layout.getLineWidth(i)) {
                        maxWidth = (int) layout.getLineWidth(i);
                    }
                }
                mTextRect.right = maxWidth;
            }

            mTextRect.offsetTo(0, 0);
            if (availableSPace.contains(mTextRect)) {
                // may be too small, don't worry we will find the best match
                return -1;
            } else {
                // too big
                return 1;
            }
        }
    };

    /**
     * Enables or disables size caching, enabling it will improve performance
     * where you are animating a value inside TextView. This stores the font
     * size against getText().length() Be careful though while enabling it as 0
     * takes more space than 1 on some fonts and so on.
     *
     * @param enable
     *            enable font size caching
     */
    public void enableSizeCache(boolean enable) {
        mEnableSizeCache = enable;
        mTextCachedSizes.clear();
        adjustTextSize(getText().toString());
    }

    private int efficientTextSizeSearch(int start, int end,
                                        SizeTester sizeTester, RectF availableSpace) {
        if (!mEnableSizeCache) {
            return binarySearch(start, end, sizeTester, availableSpace);
        }
        String text = getText().toString();
        int key = text == null ? 0 : text.length();
        int size = mTextCachedSizes.get(key);
        if (size != 0) {
            return size;
        }
        size = binarySearch(start, end, sizeTester, availableSpace);
        mTextCachedSizes.put(key, size);
        return size;
    }

    private static int binarySearch(int start, int end, SizeTester sizeTester,
                                    RectF availableSpace) {
        int lastBest = start;
        int lo = start;
        int hi = end - 1;
        int mid = 0;
        while (lo <= hi) {
            mid = (lo + hi) >>> 1;
            int midValCmp = sizeTester.onTestSize(mid, availableSpace);
            if (midValCmp < 0) {
                lastBest = lo;
                lo = mid + 1;
            } else if (midValCmp > 0) {
                hi = mid - 1;
                lastBest = hi;
            } else {
                return mid;
            }
        }
        // make sure to return last best
        // this is what should always be returned
        return lastBest;

    }

    @Override
    protected void onTextChanged(final CharSequence text, final int start,
                                 final int before, final int after) {
        super.onTextChanged(text, start, before, after);
        reAdjust();
    }

    @Override
    protected void onSizeChanged(int width, int height, int oldwidth,
                                 int oldheight) {
        mTextCachedSizes.clear();
        super.onSizeChanged(width, height, oldwidth, oldheight);
        if (width != oldwidth || height != oldheight) {
            reAdjust();
        }
    }
}

Answer 1

您的代碼有點混亂。 在清單xml中，您將其稱為“活動”，但是Java代碼用於View。 這是兩件事。 一個Activity必須派生自Activity（或其子類），並且必須具有默認的構造函數-通常它沒有構造函數，並允許編譯器生成默認的構造函數。 一個View必須至少具有3個構造函數之一，並且通常具有一個接受Context和AttributeSet的構造函數。 您的代碼所具有的。 您需要創建一個真實的Activity並將此View放入布局中以顯示。

Answer 2

為您的類創建一個不帶參數的默認構造函數。

public AutoResizeTextClock() {

}

Answer 3

默認構造函數 ：

默認構造函數是沒有參數的構造函數，或者如果有參數，則所有參數都具有默認值。 如果對於類A不存在用戶定義的構造函數，並且需要一個構造函數，則編譯器會隱式聲明一個構造函數A :: A（）。 此構造函數是其類的內聯公共成員。

因此，只需添加：

public AutoResizeTextClock() {

}

Answer 4

除了以上兩個注釋：

請記住要使用默認值初始化上下文，attributeset和defStyle，否則將無法正確設置基類。